The Belgian midfielder scored his first goal for the Red Devils in Monday night's 2-2 draw clash at the Hawthorns with - a cracking right-footed shot from inside the 18-yard-box - only three minutes into the second-half.
After the battle at West Brom, the 26-year-old showed Louis van Gaal his willingness to prove his worth after a terrible debut season at Old Trafford which saw United finish outside the Champions League spot for the first time in two decades.
However, Manchester United legend McGrath is convinced that the Belgian will sooner or later leave United due to the amount of players in Louis van Gaal's disposal, as they all fight for a starting place in the Dutchman`s team.
"United fans haven't seen the best of him because he has never really played in his best position. Only probably once or twice has he played up front," McGrath told talkSPORT.
"He showed last night it is possible for him to have a presence at Manchester United but, with the abundance of talent we have got up there, he may never get that chance.
"It is a pity for him that he is put in midfield. He did change the game last night because he put himself about, but I don't think his future would be at Manchester United, I really don't."
Written by @Chukkymufc