LONDON -- Arsenal goalkeeper Petr Cech will miss three to four weeks with a "serious calf injury," Arsene Wenger has said.
Cech, 33, was injured in the last moments of Wednesday's 2-1 loss to Swansea when he ran up the pitch for a corner as the Gunners pushed for an equaliser.
Wenger had already said Cech would miss Saturday's crucial North London derby against Tottenham, but revealed on Friday that he could be out for up to a month.
Wenger said Cech also had a minor groin injury before the game that may have hampered him as well, but that he did not regret the decision to play the keeper.
"He declared himself 100 percent fit [before the game], and then you have to trust the player," Wenger told a news conference. "He's 33 years old, and he knows his body.
"You want the players to be tough enough to play sometimes through little pains because you're never completely perfect in March before a game. So he took that very well, and I respect that."
Cech's injury means David Ospina is set to play in some of Arsenal's most important games of the season, including the round-of-16 second leg at Barcelona in the Champions League later this month.
However, the Arsenal manager said he has full confidence in his backup goalkeeper.
"If you look at the win-rate of Ospina, it's very good as well. So honestly, I'm not worried at all about that," Wenger said.
Cech looked far from his best on both of Swansea's goals on Wednesday.
Their equaliser came after the visitors won the ball by the halfway line from the keeper's clearance and went on a quick counter-attack. For the winning goal, he let an inswinging free kick get past him for Ashley Williams to turn into the net.
"On the first goal he could not kick the ball out properly because of his groin and maybe compensated a bit too much and maybe provoked another muscular injury," Wenger said.
Gunners centre-back Laurent Koscielny will also miss the Tottenham game with a calf injury but is expected back next week.
"I don't think he'll be available on Tuesday [for the FA Cup replay against Hull], but Saturday he should be all right," Wenger said, referring to the Premier League meeting with West Brom on March 12.
The Arsenal boss also said Jack Wilshere is still three to four weeks away from returning from a leg fracture he sustained before the season, but that the midfielder could be ready for a return after the international break.
England boss Roy Hodgson said on Thursday he still wants Wilshere in the squad for Euro 2016, and Wenger thinks his player will be ready for the tournament.
"He's an important player in the plans of Roy Hodgson. I know that because I spoke to Roy about Jack," Wenger said. "We first of all do everything to make him available for us, and as well for England."