The midfielder suffered strained ligaments in his wrist and it was thought he might require an operation immediately, ruling him out until December.
But Fellaini has linked up with the Belgium squad, ahead of their clashes with Croatia away on Friday and Wales at home next Tuesday, and trained with a protective cast on his wrist.
Belgium coach Marc Wilmots had been quoted as saying that Fellaini has ligament damage and requires surgery but would be able to play on Friday.
Reports also emerged suggesting Fellaini, who joined United from Everton on transfer deadline day, will delay having an operation until December.
An article on United's official website on Tuesday afternoon said: "Marouane Fellaini has trained with Belgium wearing a protective cast on his injured wrist.
"Although some reports suggest the midfielder faces an operation and a spell
on the sidelines, the deadline-day arrival is due to play in a splint against
Croatia and Wales in the World Cup qualifiers."
Fellaini picked up the injury during last Wednesday's 1-1 Champions League draw at Shakhtar Donetsk and subsequently sat out Saturday's 2-1 victory over Sunderland.