Big blow: Arsenal’s Petr Cech ruled out for up to a month

Ahead of the North London Derby against Tottenham on Saturday (Watch live, 7:45 a.m. ET on NBCSN and online via Live Extra), Arsenal’s worst fears have been confirmed.

Petr Cech is out injured for a up to a month as Arsene Wenger confirmed the Czech Republic international suffered a calf injury in the dying stages of Arsenal’s defeat to Swansea City on Wednesday.

[ PLAYBACK: Who wants to win PL? ]

Cech, 33, has been an inspired signing this season and has improved Arsenal’s defense drastically after joining from Chelsea last summer.

However, Wenger must now prepare for a crucial stretch of games without the Gunners’ leader in defense but is confident David Ospina can step in: “I trust Ospina completely,” Wenger said.

Speaking to Arsenal.com, Cech has full faith that Ospina will replace him expertly.

“David is a very experienced goalkeeper. He has played really well, especially in the FA Cup games where he has been vital,” Cech said. “I think everybody at the club, including the staff and the players, has big confidence in him because we can see in training and in his international games that he is a great goalkeeper. We have full confidence in him and it won’t be a problem. He has enough experience to play this type of game and he has played this game before so I think he will be fine.”

Arsenal will also be without Laurent Koscielny who won’t return in time, as Gabriel and Per Mertesacker will likely start at center back.

Wenger also revealed Jack Wilshere will return in three to four weeks after not kicking a ball this season.

Heading into Saturday’s NLD, Arsenal trail bitter rivals Spurs by three points in the Premier League table and league-leaders Leicester City by six points.

Follow @JPW_NBCSports