The Croatian is reportedly the next name on Jose Mourinho's transfer-list, and United have been linked with a fee of around £45m for the 28-year-old.
However, Marcotti thinks that Perisic lacks consistency and he might struggle in Mourinho's squad.
"He's certainly a very skilful player and when he's consistent, he's outstanding," Marcotti said on ESPN FC.
"He certainly hasn't always been a consistent player. My concern is, I just look at the players Manchester United have and I wonder how is everybody going to fit together?
"Martial is still there, you've got Mkhitaryan, you've got Juan Mata and that's before we get into (Paul) Pogba, (Ander) Herrera, guys like that.
"I don't know. If Mourinho wants another option that's fine. He's certainly busy and he has quality when he's good."