London: Arsenal manager Arsene Wenger has confirmed that midfielder Alex Oxlade-Chamberlain has been sidelined for weeks after suffering a knee injury in Tuesday night's 2-0 Champions League last-16, first leg defeat by Barcelona. In a news conference ahead of Sunday's Premier League game against fifth-placed Manchester United, Wenger also struck a note of caution over forward Danny Welbeck, who made his third appearance of the season against Barcelona after returning from a long-term knee injury. Chamberlain limped off after colliding with Barcelona's Javier Mascherano and although Wenger described the injury as serious, he was optimistic that it would not rule the 22-year-old out of the European Championship in the summer. "We lost Chamberlain on Tuesday night and his injury is quite serious and keeps him out for a few weeks," the manager said. "When he was cut in two by Mascherano he hit his knee and we have to see how big the damage is. He is seeing a specialist. Let's hope that we get good news and it's only two or three weeks and not six or seven." Central defender Gabriel is close to returning from a hamstring injury that has kept him out for three weeks but will be tested over the next two days before he is included in the squad for the trip to Old Trafford. On Welbeck, Wenger said: "(He)is back in the squad but we have to be cautious with him. He has been out and he is not completely over his knee problem. He is doing extremely well, he is very fit but I have to analyse (if he can start)." Arsenal are third in the table, two points behind leader's Leicester. They trail North London rivals Tottenham Hotspur on goal difference.