Fletcher, 28, has not appeared for United since November 2011 when he was given an extended break from the game due to ulcerative colitis, a chronic inflammatory bowel condition.
However, the Scotland international played 90 minutes in a friendly against Stalybridge Celtic on Tuesday evening and has now been welcomed back into the first-team fold.
Sir Alex Ferguson said: "Darren's in the squad tomorrow, simply because I think it will give him a boost.
"It's a chance to progress. At this moment in time everything's going fine for him."
Ferguson also had further good news regarding summer signings Shinji Kagawa and Robin van Persie, both of whom sustained injuries during the international break but are fine for the game against Wigan.
However, Ferguson revealed that England international Jones could now be sidelined for as much as 10 weeks after undergoing knee surgery.
Initial estimates put his recovery time at six to eight weeks but the problem is more serious than United first feared.
"Jones was a bad blow for us. He got an injury in training last weekend and he'll be out for eight to 10 weeks.
"We expect Smalling to be back training inside a month. There's a little bit of comfort in that sense, given our centre-back situation. But with Jonny [Evans] back we're in a better position than we were a couple of weeks ago."
Ferguson also called for an end to the hostility between Manchester United and Liverpool.
The north west giants have a long history and a bitter rivalry both on and off the pitch.
But following this week's release of the Hillsborough Independent Panel's report - which cleared Liverpool supporters of any blame in the 1989 tragedy in which 96 supporters died - Ferguson is keen for a better relationship and more friendly rivalry to develop.
"We are two great clubs, ourselves and Liverpool," said Ferguson, ahead of Saturday's clash with Wigan.
"We should understand each other's problems. Maybe a line will be drawn in the sand in terms of their behaviour towards each other."