The Belgian completed the move from Everton on Monday.
And expectations are high given the exorbitant price United paid for the 24-year old.
The Red Devils have reportedly paid £75m up front, but the fee could rise to £90m, if bonuses are met.
"I think that if he can handle the pressure then that is one aspect of being a No 9 at Manchester United," Marriner told ESPNFC.
"But the biggest ask that I have about Lukaku is in those tight areas, when teams are going to sit in, when teams are going to defend deep, has he got the quick feet to open up defences and finish? I don't know.
"It is a no at the moment, I hope he does well. At the moment, from what I've seen at Everton, I don't see him being a success."