Yacob sustained the injury during West Brom's 1-1 draw with Chelsea at The Hawthorns earlier this month.
However, the Argentinian may be back for the March 8 clash with the champions as Mel seeks his first win in charge of the club.
"It is possible Yacob will be available to play against United," he told the club's official website.
"He is a very important player for us in the middle. He is strong and is playing well.
"It is important for us to play with three midfielders because now for us it is better."
Mel also confirmed the state of play with on-loan forward Scott Sinclair, who has played just one half of football since the coach's arrival.
"On Friday Scott Sinclair spoke with me," the Spaniard continued.
"I told him he is a good player, a good winger.
"At the moment West Brom need hard work on the pitch. But I assured Scott Sinclair he will play in the future.
"It is normal he is disappointed he is not playing. But I can only pick 11 and it is difficult every day."
