By Arsenal correspondent Tony Hughes

Gabriel will undergo tests ahead of Arsenal’s showdown against Manchester United.

Manager Arsene Wenger has confirmed that the Brazilian is back in training but will have to prove his fitness to be selected for Sunday’s Premier League clash at Old Trafford.

Gabriel has missed the last three Arsenal matches with a hamstring injury and returned to Brazil to undergo treatment.

Speaking at his media briefing on Friday, Wenger said: “Gabriel has a test today and tomorrow and then we will see if he is available for the game.”

In other Arsenal injury news, Wenger has revealed that Alex Oxlade-Chamberlain will see a knee specialist about the injury he sustained in Tuesday’s Champions League defeat to Barcelona and admitted the midfielder could face a lengthy spell on the sidelines.

We lost Chamberlain on Tuesday. His injury is quite serious and keeps him out for a few weeks. He’s seeing a knee specialist.”

Asked when the 22-year-old will be back, Wenger said it could be “two or three weeks” or perhaps even “six or seven”.