Schalke head coach Jens Keller has admitted Christian Fuchs and Felipe Santana are in doubt for his team's trip to Mainz on Saturday.
Austrian full-back Fuchs has played 90 minutes for Austria against both Germany and the Republic of Ireland over the past week and has returned to Gelsenkirchen with an injury, while Brazilian central defender Santana is sick.
Meanwhile, Dutch striker Klaas-Jan Huntelaar remains unavailable for selection due to the knee injury he sustained in Schalke's 4-0 loss to Wolfsburg on August 17.
"We can't really tell yet (who will play against Mainz), Christian Fuchs came back with slight injury, he trained a bit but couldn't finish," Keller said.
"Then Felipe Santana has come down with the flu, we have to wait now.
"Klaas-Jan is still not an option for Saturday, other than that, everyone else came back from the internationals fit and healthy."
Schalke will enter Saturday's game at Mainz's Coface Arena in 13th spot on the Bundesliga table with just three points from four rounds.
The North-Rhine Westphalia club lost their opening three games of the Bundesliga season before they overcame Bayer Leverkusen 2-0 before the international break.
By contrast, Mainz sit fifth on nine points with three victories and Keller knows what to expect from Thomas Tuchel's energetic side.
"They will be very aggressive for the first 20 minutes, they will attack from the front, they will show a huge amount of effort," Keller said.
"Tactically they have improved and have good ideas around their team."
Schalke have a busy period coming up with seven games in three weeks, including two UEFA Champions League matches and a DFB Pokal tie.
But Keller would not have it any other way and cannot wait to lead Schalke in the Champions League.
"We wanted to reach a stage where we can play international matches during the week and that's what we have done," Keller said.
"We are looking forward to hearing the Champions League hymn on a Tuesday or Wednesday evening, I think every player wants that."
|Coach: T. Tuchel|
for S. Okazaki 57'
for E. Soto 76'
for C. Moritz 76'
|´It was far from a friendly´ - Klopp on Chelsea defeat|
|Madrid off the pace, concedes Zidane|
|Chelsea 1 Liverpool 0: Cahill´s header seals win|
|Grujic says Chelsea´s Matic told him to sign for Liverpool|
|Bolasie wants to see Berahino and Benteke at Crystal Palace|
|Rodgers hails ´outstanding result´ as Celtic draw|
|Walcott claims level of MLS is close to Premier League|
|Bayern Munich 3 AC Milan 3 (3-5 on penalties): Bonaventura seals win|
|Atletico Nacional 1 Independiente del Valle 0 (2-1 agg): Borja secures Copa Libertadores crown|
|Icardi absent again as Inter held by Estudiantes|
|Real Madrid 1 Paris Saint-Germain 3: Zidane oversees poor pre-season start|
|Hazard vows to rediscover best Chelsea form|
|Klopp reveals why he sent Sakho back to Liverpool|
|Tevez: Conte wanted me at Chelsea|
|Sunderland hopeful Defoe will be fit for Man City opener|
|Sundowns overcome Zamalek to book semi-final spot|
|Falcao scores as Monaco return ends in defeat to Fenerbahce|
|Southampton overcome Twente, Asoro stars for Sunderland|
|Man City must adapt to Guardiola tactics quickly - Denayer|
|Chelsea and Leicester to play in EFL Trophy as five Premier League clubs refuse|
|Tolisso pulls plug on €37.5m Napoli move to stay at Lyon|
|Ancelotti shrugging off Guardiola´s shadow|
|Uruguay international Lodeiro swaps Boca for Seattle|
|Ibrahimovic will bring United back to where they belong - Larsson|
|Transfer speculation frustrates Aubameyang|
|Willian ready for ´toughest Premier League season in history´|
|Astana 1 Celtic 1: Griffiths hits late equaliser|
|De Laurentiis feels betrayed by Higuain swapping Napoli for Juventus|
|Costa: Chelsea cannot be any worse than last season|
|Wilshere: Xhaka can hold Arsenal midfield together|
|Pato signs four-year deal with Villarreal|
|Higuain sets sights on Champions League after Juventus move|
|Lazio snap up Immobile from Sevilla|
|Batshuayi worth the money, insists Cahill|
|Arnautovic signs new Stoke deal|
|Smith leaves Liverpool for Bournemouth|
|Barcelona insist Arda Turan will stay|
|Andre Gomes: Barcelona suit my identity better than Real Madrid|
|Niersbach to appeal FIFA ban|
|Barcelona agree Mascherano renewal|
|Fernandinho can play in 10 positions - Guardiola|
|Reading´s kit launch is out of this world|
|Ben Arfa: I do not want to be PSG´s star player|
|FA Cup to trial fourth substitute|
|We want Balotelli and he wants us, says Besiktas chief|
|Crowd welcomes Higuain as he arrives for Juventus medical|
|Guardiola warns Man City stars: If you´re not fit, danger is coming|
|Mkhitaryan prepares to prove himself at United|
|Cavani: No pressure replacing Ibrahimovic|
|Wenger vows to keep transfer plans ´secret´ after Lacazette snub|
|Brannagan open to Championship loan move|
|Wenger wants to sign Mertesacker replacement|
|Ancelotti: Bayern´s transfer business done|
|Brisbane Roar sign former Danish international Kristensen|
|Verratti, Luiz missing for PSG|
|Sounders part ways with foundation coach Schmid|
|Mane turned down Manchester United for Liverpool|
|Zidane on Pogba: Until August 31, anything can happen|
|Mkhitaryan driven by father´s death|
|Inter rejected Napoli offer for Icardi, says president|
|Clichy: City fighting fit after Guardiola pizza ban|
|Everton and Burnley win as Hull are held|
|Ajax held by PAOK after Cillessen howler|
|Conte left frustrated by ´crazy´ money in transfer market|
|Neymar makes Barcelona case to Gabriel Jesus|
|Rostov comeback twice for Champions League draw with Anderlecht.|
|Arsenal defender Mertesacker set for lengthy lay-off|
|Conte not selling ´fantastic´ Matic|
|Ibrahimovic keen on MLS and Beckham´s Miami project|
|Neymar: I play for Messi, he´s the man|
|Barcelona reveal details of Andre Gomes deal|
|Suarez bullish over Barcelona prospects|
|Ajax claim Napoli keen on Milik to replace Higuain|
|Totti labels Higuain´s Juventus move ´a disaster´|
|Juventus confirm Higuain deal|
|Pato to Villarreal ´in the final stage´|
|PSG sign Lo Celso|
|Muller: Beating Dortmund will be more fun this season|
|Juventus sign Higuain from Napoli for €90m|
|Pastore: I´m like God in Paris|
|Injured Lanzini out of Olympics|
|Allegri unperturbed by Higuain fee|
|Menezes replaces Bento at Cruzeiro|
|Sporting rejected major bids from Inter and Liverpool for Joao Mario, claims father|
|Pochettino pleased by Tottenham despite Juventus defeat|
|Eriksson: Allardyce the right man for England|
|Mourinho makes United train after stepping off plane from China|
|Hazard can still match Messi, says Pedro|
|Pjanic shows there is life at Juve, with or without Pogba|
|Juventus 2 Tottenham 1: Benatia bags win for Serie A champions|
|Dembele: I am not the Bundesliga´s next superstar|
|Lyon claim €35m Arsenal offer for Lacazette rejected|
|Donnarumma dreaming of Milan captaincy as he eyes long-term stay|
|Robson: Ibrahimovic can match Van Persie´s first year at United|
|Rooney should remain England captain - Eriksson|
|Emery wants new striker at PSG|
|Santos accept Juventus bid for Gabriel|
|Eriksson expects Sweden to try and tempt Ibrahimovic out of retirement|
|Spurs signing Janssen almost quit|
|Leicester stay best for Mahrez - Ranieri|
|Allardyce to take Mourinho cue on Rooney|
|Ings ready to outdo big-money signings|
|Henderson optimistic over Liverpool campaign|
|Allardyce hardened to the challenge of England post|