The midfielder, 30, notched his third goal of the season in Tuesday night's 1-0 FA Cup win at Rochdale, to send the Shrimps into the second round.
With the Scot now having already matched last season's goalscoring tally, Bentley believes McDonald can perform a similar role to New York Red Bulls midfielder Cahill in providing the attacking thrust from midfield.
Bentley told BBC Radio Lancashire: "We've been working on the timing of runs and sometimes he goes in and just stands in there.
"I asked Gary to be on the move. Cahill was the best at it.
"That's what he's done. He came onto the ball perfectly and it's got us the win."