Arsène Wenger has suggested that Cesc Fábregas and Robin van Persie will struggle to be fit for Arsenal's opening game of the Premier League season, against Liverpool at Anfield two weeks on Sunday. The manager has also effectively confirmed that he is in negotiations with Werder Bremen over the transfer of the Germany centre-half Per Mertesacker.

Fábregas and Van Persie played in the World Cup final on 11 July, for Spain and Holland respectively, and Wenger has granted them extended summer leave in light of their exertions. They are not due to report back to the training ground until next Thursday, meaning they will miss this weekend's Emirates Cup, when Arsenal play Milan and Celtic, and, almost certainly, the club's final pre-season fixture, at Legia Warsaw on Saturday week.

"Fábregas and Van Persie are due to come back on 5 August and from then on we will see how much build-up work is needed physically and as well how they have recovered mentally from the World Cup," Wenger said. "They might be short for the first game [of the season] but I don't know. That will depend on the fitness work that they have done during the holiday."

Arsenal, who have seen Sol Campbell turn down a new contract to sign for Newcastle and with William Gallas and Mikaël Silvestre having been released, are also short of options in central defence, despite the addition of Laurent Koscielny.

Wenger was asked whether he wanted to sign Mertesacker, 25 and who played for Germany at the World Cup finals and has two years to run on his contract at Bremen. "There are people we consider and are analysing and we look at the financial possibilities," he replied. "We are still on the search for centre-halves. We have three and we need at least four."

One of them is Johan Djourou, who missed all but the final match of last season because of a knee-ligament injury and the 23-year-old gave Arsenal a scare when he was forced out of Tuesday's win over SC Neusiedl with a hamstring problem. However, it was not serious and Wenger expects the defender to be fit for the weekend. "It is not bad," he said. "He should be available."

It is the club's official photo-call next Thursday and Arsenal will take great delight in picturing Fábregas in this season's colours, in the wake of Barcelona's concerted bid to lure him back to Catalonia.

On the subject of Barcelona and Fábregas, Wenger added: "It is only noise. In our job, we have to deal with what we can master. What we cannot influence is not to worry about. We have learned about that and I believe that in a big club you have to live with those kind of noises without being disturbed.

"I am very happy with Cesc and we are all very happy at the club with Cesc. He is a very important player for us, he is our captain and we have worked very hard [for him] to be the future of our team and that is why we are always adamant about [not] letting him go."