The England striker suffered the injury during the second half of the 1-1 draw with Bayern at Old Trafford last Tuesday. United face the German champions in the return on Wednesday. (Agencies)
"Wayne's got a badly bruised toe," Moyes told MUTV on Friday. "He picked it up in the game the other night. Whether we were going to play him or rest him, it doesn't matter.
"He's got a terrible toe and not only will it be a problem for this game, it could be a problem for the Munich game as well on Wednesday. So we need to monitor it. We'll get him treatment all over the weekend and see if we can speed it up."
United, seventh in the league, are already missing first-choice striker Robin Van Persie for up to another four weeks with a sprained knee he picked up after scoring a hat-trick against Olympiakos Piraeus in the Champions League last month.
"It will be touch and go for Wayne for Wednesday," Moyes told reporters. "It's a toe injury and they are never easy. You could see him limping in the game towards the end quite badly.
"There is not an awful lot you can do with a toe injury. Sometimes you can feel better quite quickly with them and sometimes you need an injection possibly to play with it if it is bruising," Moyes was quoted as saying by British media.
"With a lot of toe injuries you have to make sure there isn't a hairline fracture or crack in your toe. We will have all that checked."
The England striker suffered the injury during the second half of the 1-1 draw with Bayern at Old Trafford last Tuesday. United face the German champions in the return on Wednesday.