Alex Oxlade-Chamberlain will have a scan on Thursday to assess injuries picked up against Barcelona on Tuesday.
Oxlade-Chamberlain was involved in a heavy high-speed challenge with Javier Mascherano which left the two players in pain during Arsenal's 2-0 Champions League last-16 first-leg defeat at the Emirates.
Despite playing on with a noticeable limp for the remainder of the first half, Oxlade-Chamberlain did re-emerge at the start of the second half before quickly coming off.
The 22-year-old reportedly left the ground on crutches with his right leg heavily strapped and the fears are that he has both knee and ankle damage.
However, Arsenal manager Arsene Wenger told the club website that he has not ruled out the England international any further than their match against Manchester United at the weekend.
"He has a scan today (Thursday), he will not be available for Sunday," said Wenger.
The midfielder's career has been plagued with various injuries, and there are fears another another set-back will see him miss out on friendly European clashes against Holland and Germany next month.
He missed the last World Cup in 2014 with an injury to his right knee, and towards the end of last year struggled with a hamstring problem.
Meanwhile, defender Gabriel is set to return to training on Friday following a hamstring injury and could be involved at Old Trafford.
"He is coming back into the squad tomorrow, so we will see how he responds to that, but the signs are positive," added Wenger. "He might be available for Sunday."