• Costa Rica striker injured knee at Gold Cup in July • Campbell one of 28 senior players at club, three more than league limit

Joel Campbell, Arsenal’s forgotten man, is back at the club and he has made it clear that he is reluctant to go out on another loan. The 25-year-old Costa Rica striker is under contract until 2019 and his situation has been complicated by a knee injury he sustained in a Gold Cup tie for his country against Canada on 12 July.

Campbell returned to Arsenal’s London Colney training base on Monday and he is working to rebuild his fitness. It is unclear how far short of the required level he is, at present.

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He joined Arsenal as a 19-year-old from Deportivo Saprissa in 2011 but he made his debut for the club in August 2014 – after starring for Costa Rica at the Brazil World Cup – having spent season-long loans at Lorient, Real Betis and Olympiakos.

The striker featured in 10 games for Arsenal in the first half of the 2014-15 season before joining Villarreal on loan for the second half of that campaign. He extended his contract at Arsenal before the move to Villarreal. Campbell enjoyed a full season in Arsenal’s colours in 2015‑16, scoring four goals in 30 appearances in all competitions, but he spent last season back on loan at Sporting Lisbon.

Campbell is one of 28 senior players in Arsène Wenger’s squad, which is three more than the Premier League limit, and he numbers among the 17 non-homegrown players, which is on the limit.

Wenger is working to trim the squad and talks are being held between the club and Galatasaray over the left-back Kieran Gibbs. The manager is open to offers for a clutch of others, chief among them Mathieu Debuchy and Lucas Pérez, while he is expected to loan the under-21 players Krystian Bielik and Jeff Reine-Adelaide. Deportivo La Coruña want Pérez but they have so far been unable to agree a fee for him.

The defender Calum Chambers, who spent last season on loan at Middlesbrough, had been close to a permanent move to Crystal Palace but Wenger could now keep him, having sold Gabriel Paulista to Valencia. If he were to move on Gibbs and Debuchy, Wenger would have eight specialist senior defenders, including Chambers – and he is conscious that Per Mertesacker will retire at the end of the season. Chambers, himself, expects to stay. He is currently struggling with a groin injury but is expected to be fit after the international break.

Arsenal’s 28 senior players

Goalkeepers Cech, Ospina

Defenders Bellerín*, Chambers*, Debuchy, Koscielny, Mustafi, Mertesacker, Holding*, Monreal, Kolasinac, Gibbs*

Midfielders Ramsey*, Xhaka, Oxlade-Chamberlain*, Elneny, Wilshere*, Cazorla, Coquelin*, Özil

Forwards Sánchez, Lacazette, Giroud, Welbeck*, Walcott*, Campbell, Pérez, Akpom*

Notable under-21 players Iwobi, Maitland-Niles, Nelson, Bielik, Reine-Adelaide

*denotes homegrown player