Arsene Wenger has confirmed Arsenal goalkeeper Petr Cech will be sidelined for three to four weeks with a calf injury.
The Czech Republic international suffered the injury as he raced back towards his own penalty area after coming up for a corner in the last minute of his side's 2-1 home defeat to Swansea on Wednesday, a result which left the Gunners six points behind Premier League leaders Leicester.
Wenger admitted that Cech had a groin issue before the game but trusted him to play. Alexis Sanchez played against Norwich in November, despite knowing of a hamstring problem which then flared up in the game and ruled him out for the festive period.
Ahead of Saturday lunchtime's north London derby at Tottenham, Wenger said: "Cech will be three or four weeks with a calf injury.
"It is a serious calf injury and he had a groin alert on the first goal and he could not kick the ball properly out because of his groin and maybe compensated a little too much and provoked another muscular injury.
"We had to make the decision before the game because he had a little groin problem but he declared himself 100 per cent fit. Then you have to trust the player. He's 33 years old and he knows his body. If he says he's fit, then he is available.
"It is like it is. I focus on the future. You want the players to be tough enough to sometimes be able to play through a little pain. You're never completely perfect before a game in March."
Cech's absence thrusts Colombian World Cup goalkeeper David Ospina into the spotlight but Wenger insists he has no concerns on that score.
"I have complete confidence in David and I'm not worried at all on that front," he added. "If you look at the win-rate of Opsina, it is very good as well.
"Laurent Koscielny is also out on Saturday and maybe a doubt for Tuesday [FA Cup replay at Hull]."