Arsenal are fretting over the fitness of midfielder Alex Oxlade-Chamberlain after the England international limped off during the Premier League win over Southampton at St Mary's.

Alexis Sanchez and Olivier Giroud netted second-half goals to lift the Gunners above Manchester United and into fifth, three points off the Champions League places, as they took advantage of their game in hand over other teams – but injury again threatens to overshadow their success.

Oxlade-Chamberlain went off after 36 minutes with what manager Arsene Wenger confirmed was a hamstring injury. The ex-Saints youngster has featured 43 times this season, scoring six goals and making 11 assists, but with less than three weeks of the campaign remaining his participation during the remainder of the season has been thrown into doubt.

"No, not really," Wenger told Sky Sports when asked if he knew the severity of the injury. "He has done his hamstring, but how bad it is, I do not know."

Oxlade-Chamberlain joins defender Laurent Koscielny and playmaker Santi Cazorla on the Arsenal treatment table with four games – including the FA Cup final against Chelsea – to come this term.

It is a season that could yet see Wenger maintain his 100% record of qualifying for the Champions League in each of his 20 terms in charge at Arsenal. A tight game against Claude Puel's side was blown open by a piece of brilliance from Sanchez, who took his top-flight tally to 20 – the fifth player to reach the milestone for the club in the history of the Premier League – after turning inside two Saints defenders before firing past Fraser Forster.

Giroud came off the bench to score his sixth goal as a substitute this season, and his 14th in all, to secure the win which takes Arsenal into fifth in the table and three points off the top four.

They trail Liverpool by just four points and have a game in hand over Jurgen Klopp's men ahead of the final three games, starting at Stoke City on Saturday [13 May].

Alex Oxlade-Chamberlain
Alex Oxlade-Chamberlain limped off on his return to St Mary's Reuters

"I am very pleased because we had a consistent performance from the first to the last minute," said Wenger. "We were quick, dynamic going forward and well organised.

"It was a difficult game, which we expected, but overall I believed in the second half we could score the goals which we did not in the first half, because we created space and it was a very convincing win.

"We had some chances in the first half, it was a very even game. In the second half we took over and created many opportunities to score. Alexis is a player who never gives up and is always tricky to stop and very good in short space. When he has the ball in the box he is dangerous.

"Alexis always grows during the game. He is a slow starter and he gets stronger and stronger. [Giroud] has been amazing for us. It is difficult for me at the moment. Welbeck and Giroud; both of them played well. Both of them have great team spirit as well. I am always harsh with the one that doesn't play. We know what we want to achieve: we can just focus on our next game now."