The 36-year-old suffered a recurrence of a hamstring injury in the 2-2 draw with West Brom at the weekend, after just having returned from a two-week injury lay-off.
“The loss of Ryan as a wide player was a big one for us. He has done his hamstring again,” United boss Sir Alex Ferguson told MUTV.
“He got it against Bolton but trained all week and had been doing very well, but it has gone again and maybe we need to give him a longer recovery.”
