A tired Ibrahimovic was dropped to the bench for Sunday's 2-0 win and his replacement Rashford opened the scoring after seven minutes.
The goal was part of an impressive all-round display by the young striker which led critics to suggest United were better without Ibrahimovic.
Manchester United player ratings against Chelsea Sun, April 16, 2017
Express Sport rates how the Manchester United players performed during their win over Chelsea at Old Trafford
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Which Manchester United players impressed during their win over Chelsea?
But the 35-year-old remains United's top scorer this season and Carragher thinks he can still contribute at Old Trafford.
Carragher said on Sky Sports: "You shouldn't get carried away with one game.
Manchester United's Zlatan Ibrahimovic
"Zlatan has been one of the best players in the Premier League this season.
"Does he lack mobility? Yes, you know that when you sign him. The whole point of United having fast wingers and Rashford playing wide at times was to give you that [mobility]. You know Ibrahimovic hasn't got that pace when you sign him.
"Do they play better? If Rashford played centre forward next season I don't think he'd get the goals Zlatan has got. He may provide other things and help other players but let's not forget it's just one game, Zlatan has been outstanding this season."
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