United, who have been drawn in Group H with Braga, Galatasary and CFR Cluj, have to submit their 25-man squad for the competition to UEFA by Monday.
"Darren could come into the 25-man Champions League squad quite easily, without me having to leave others out because we have a number of players who qualify as youth products in addition to the 25," Ferguson said on the club website.
"He's training well, every day. I think he's going up to Scotland again next week to work with them [the national squad]. He played the other night for the Under-21s and played really well.
"With the condition he has, though, it's a case of wait and see. If he keeps doing as well as he's doing then obviously he'll be under consideration because he's a fantastic player," added Ferguson.
Fletcher, who has ulcerative colitis, last played for United in November during a Champions League match against Benfica.
Ferguson also confirmed Wayne Rooney would be out of action for only four weeks after suffering a gash to his thigh in last weekend's win over Fulham.
"It's nothing serious on the actual gash - it's a bad one but it was treated carefully very quickly. We don't expect any complications from it. I think he'll be back in four weeks," Ferguson said.
"The fact it's a gash and not a muscle or joint injury means he can do a lot of work in the gymnasium."
