Arsenal manager Arsene Wenger says Per Mertesacker is fully fit but will have to fight to secure a regular place in the squad.
The Germany international was not even on the bench for Saturday's game against Stoke City but is expected to be back in the squad for the mid-week Champions League game away at Dinamo Zagreb.
The Frenchman also gave an update on the fitness level of Danny Welbeck and Jack Wilshere with the midfielder to be assessed at the end of next week.
"He [Per Mertesacker] should not worry," Wenger said after the Stoke City game.
"He should just come back and play. It is good we have four centre backs and this produces a problem. If Walcott plays and scores everybody says that Walcott is good but before the game everybody says I should buy a striker but if I had a bought a striker then Walcott would not have played.
"So it is always a vicious circle and at some stage you just have to believe in your players and Gabriel has shown that he can play with Mertesacker, he can play with Koscielny and he can be a great defender.
"[Danny Welbeck's injury] was a shock of course. I think Welbeck can play in every position up front and he is a fantastic guy.
"To see him work for three or four months and then be ruled out again for three or four months is difficult to understand but we have to deal with that. I can understand that people say that we have to look out for a striker but we honestly did not find anyone.
"[Jack] Wilshere progresses slowly. We will know more about Jack in the next few days and hopefully it will be good news but he progresses."