Against Marseille a week-last-Wednesday, Dimitar Berbatov didn't even get off the bench as Fergie preferred Rooney and Hernandez up front.
And Macari told the Daily Star Sunday: "The front two is the manager's decision.
"Whichever pairing he plays up front, you've got to go with that. It's Rooney at this moment in time with Little Pea.
"Antonio Valencia is back and he will provide plenty of balls into the box for them. When Berbatov gets his chance he's going to have to take it. I guess it's a nice problem for the manager to have."
Macari, a United player from 1973 to 1984, is also sure United will pip Arsenal to the title.
He added: "I do think they will win the league.
"They've done it before and know how to win when the chips are down."