Nigel Pearson cited Dean Hammond's withdrawal through cramp as a turning point in Leicester City's 2-0 defeat to Chelsea on Saturday.
Leicester, who held Everton to a 2-2 draw on the opening day of the season last weekend, frustrated Jose Mourinho's side for long periods at Stamford Bridge.
David Nugent had a golden chance to put the visitors in front 10 minutes after the break, but Thibaut Courtois denied the striker, who had gone one-on-one with the Belgian.
After Diego Costa had netted his second goal in as many games, Hammond was forced from the field with severe cramp, shortly before Eden Hazard made the game safe for the hosts.
"He got severe cramp right the way through his leg which he's never experienced before," Pearson said.
"It was frustrating for him because the last two games he's played very well.
"We certainly missed his organisational skills and when he went off we lost a bit of our rhythm somewhat.
"It was probably the worst timing for that to happen but these things happen in football and you've got to get on with it."
Despite the defeat, Pearson took the positives after a promising display from the visitors, who were promoted as champions of the second tier last season.
"The good thing is we created chances throughout the game and made their goalkeeper work," he said.
"We wanted to be positive and I think for the most part we played very well.
"But as always it's going to be how efficient you are in both penalty boxed and we didn't quite find the right way today."
|Mourinho takes aim at reporters as Man United boss leaves news conference|
|´Bull****´ to suggest Chelsea can catch Man City – Conte|
|Pordenone would´ve deserved Coppa Italia progression, admits Spalletti|
|Man City haven´t won anything yet – Gundogan|
|Willian: Chelsea will keep fighting for Premier League title|
|Burnley aren´t the real deal – Dyche|
|Stoger wants to bring best out of BVB after breakthrough victory|
|Conte praises contribution of Hazard, Willian and Pedro|
|Inter 0 Pordenone 0 (AET, 5-4 on penalties): Nagatomo spares Serie A leaders´ blushes|
|Hodgson keeping Palace grounded despite dramatic late win|
|Zouma injury led to Turf Moor defeat – Hughes|
|Guardiola steers carefully around Mourinho criticism after United v City flashpoint|
|Guardiola considering January signings to bolster Manchester City squad|
|Crystal Palace 2 Watford 1: Sako, McArthur stun Hornets|
|Huddersfield Town 1 Chelsea 3: Willian sparkles as Conte´s side return to winning ways|
|Burnley 1 Stoke City 0: Hosts go fourth after late Barnes winner|
|PSG escape punishment as LFP gives Lille transfer ban|
|Mainz 0 Borussia Dortmund 2: Stoger´s tenure begins with much-needed victory|
|Ten Cate: Al Jazira will park three buses against Real Madrid|
|Gremio 1 Pachuca 0 (after extra time): Everton stunner sends Brazilians into final|
|Zidane focused on Club World Cup despite looming Clasico|
|Ibrahimovic brands Guardiola ´immature´ over Barcelona row|
|Pogba has no regrets over rejecting Real Madrid|
|Gattuso denies contract rift with AC Milan goalkeeper Donnarumma|
|Pochettino: Alderweireld out until February|
|Wydad Casablanca 2 Urawa Red Diamonds 3: Marvellous Mauricio double proves decisive|
|Cardona given five-match ban for ´discriminatory´ gesture against South Korea|
|James still settling at Bayern, says Heynckes|
|Manchester City captain Kompany out for ´a short time´|
|Klopp: Liverpool need Lallana ahead of busy period|
|It was diversity in education – Mourinho addresses derby fracas|
|I encourage City to celebrate - Guardiola defends players after Old Trafford controversy|
|I´m no actor – No regrets for Klopp over heated interview|
|Everton were like United at Liverpool - Allardyce defends Anfield approach|
|Paulo Bento hired as Chongqing Lifan head coach|
|Ramsey hamstring injury ´not a big one´|
|Watford´s Zeegelaar gets three-match ban as appeal is rejected|
|Matthaus raves about Spurs star Kane|
|´Several clubs´ discussing Arda move as Barca exit nears|
|No ultimatum as Arsenal´s Ozil and Sanchez talks rumble on|
|Su-Mourinho? Wenger offers advice to City and United|
|Bayern planning ´serious talks´ with Robben, Ribery|
|Pereira replaces Villas-Boas at Shanghai SIPG|
|Van Gaal rejected Leverkusen to hold out for a ´big club´|
|Inzaghi and Lazio left feeling ´defrauded´ after Torino defeat|
|Man United more boring under Mourinho, claims Van Gaal|
|Zidane: Real Madrid want to win Club World Cup|
|Morata ruled out of Huddersfield trip due to ´impossible´ workload|
|Valverde singles out Hazard & Morata as chief Chelsea threats|
|Lazio 1 Torino 3: Inzaghi´s men lose ground as Immobile sees red|
|Reading 2 Cardiff City 2: Late comeback makes light of Warnock dismissal|
|Wagner received no contact over Borussia Dortmund job|
|A Mourinho myth? Man United booked for simulation more than any Premier League side|
|Ronaldo´s ego is his biggest motivator - Valdano|
|Bayern threaten legal action over Leno transfer rumours|
|Potter delighted by underdog Ostersunds´ trip to Arsenal|
|Chelsea can bounce back from West Ham loss, says Conte|
|Real Madrid will relish PSG test, says Xabi Alonso|
|Conte urges Chelsea to be ´positive´ over Barca Champions League draw|
|Heynckes wary of Besiktas threat|
|Ostersunds handed fairytale Arsenal tie, Napoli face Leipzig|
|Emery: PSG ´can compete with Real Madrid´|
|Totti urges Roma focus on Serie A despite encouraging Champions League draw|
|Europa League: Last 32 draw in full|
|Messi faces toughest foe in Champions League|
|AC Milan signed too many players, admits Fassone|
|Real Madrid face PSG, Chelsea drawn with Barcelona|
|FA seeking information over Manchester derby incident|
|He is one of the best strikers in the Premier League - Wilshere hails Giroud|
|Mata: No time to mourn derby defeat|
|Hitzfeld tells Nagelsmann to honour Hoffenheim contract|
|Amor: Mascherano future to become clear soon|
|Huddersfield confident of Chelsea scalp - Ince|
|De Bruyne: Man City have to enjoy derby victory|
|There is no-one like Messi – Alcacer|
|Kane: Bring on the best in Champions League|
|Neville: Lukaku needs to believe amid Man United struggles|
|Messi best player of all time – Rakitic|
|Gattuso: I´m even tense playing football with my son|
|Suarez admits Villarreal red swung it for Barcelona|
|Villarreal win ´crucial´ for Barcelona boss Valverde|