Downes has had a scan but it will be down to the consultant to identify the severity of the problem.
It is feared the 24-year-old could be set for another lengthy spell on the sidelines.
The Premier League's four representatives all face crucial matches in the final round of Champions League group games next month.
Arsenal were dealt a severe blow on Monday when it was revealed Francis Coquelin the injury the Frenchman picked up
For years, and years, and years, Tottenham Hotspur Football Club have fought tooth and nail to become a Champions League
Manchester United host PSV in the Champions League on Wednesday.
Juventus midfielder Claudio Marchisio is wary of a potential Manchester City backlash in Turin this week.