Arsenal goalkeeper Petr Cech has warned that it will be tough to replace Per Mertesacker during the opening months of the new season.

Mertesacker has been ruled out for "a few months" having sustained a knee injury during a pre-season clash, leaving the Gunners short in central defence.

Arsene Wenger is expected to venture into the transfer market in order to make up for the loss of the World Cup winner, but Cech admitted that Mertesacker's absence is a big blow for his side.

"[Mertesacker] is a great player, a great part of the team with his experience. You cannot just replace a world champion winner just like that because obviously the experience of him, the games he played and he's one of the captains. That says it all," he told ESPN.

"We will need to make sure that the players who will get their chances to play more, they will take it and they will rise to the occasion. Hopefully we will be able to start the season well and once he's fit he will come back [with us] in a position where we all want to be.

"Now with Per out, the challenge and the possibilities for every central defender is bigger. It's up to [Rob Holding] how he's going to play and how he's going to work. The same is true for Gabriel Paulista and Calum Chambers. This is their moment to show the manager they are up to the task."

Meanwhile, Francis Coquelin has hinted that he could act as a makeshift defender during Arsenal's pre-season tour of the United States.