Giggs out of Valencia trip
Wayne Rooney also picked up an ankle knock in the 2-2 draw at Bolton Wanderers but manager Sir Alex Ferguson is confident the England striker will be available for the Group C fixture.
"Ryan is the more serious injury," Ferguson told Manchester United's website.
"It's a hamstring injury and he'll be out for a couple of weeks. With Wayne, I am sure we will be able to get him ready for Wednesday."
Defender Rio Ferdinand is also expected to face Valencia despite playing no part against Bolton following recent injury problems.