Barcelona midfielder Cesc Fabregas insists he is yet to reach his best with the European champions, and feels he must improve.
The former Arsenal captain has put in several impressive displays since returning to Camp Nou after an eight-year spell at the English Premier League club, and has become an important first-team player.
But the Spain international is unhappy with his own performances and said there are changes to be made.
"I'm not happy with my own performance against Real Madrid (in Copa del Rey) last Wednesday night. I have to improve a lot," Fabregas told the Barcelona website.
"Although I was brought up to play football the Barca way, this is the boss' system and it's not easy to get it straight away. "
"When I play further forward, I have more mobility and that's a role I can handle. However, further back I need to have more discipline and I currently miss the patience for that."
The 24-year-old has made 14 La Liga appearances for Barcelona, scoring nine goals to help Pep Guardiola's team into second behind rivals Real Madrid.