The veteran Swedish striker said there was no need to put pressure on Rashford.
"First of all, he's 18, he's still young. He has a lot of time," Ibrahimovic told the club's website (www.manutd.com).
"I think the way you have to approach a player like that, where everyone is talking about the talent and what he's able to do and what kind of potential he has, is to remember he still has a lot of time.
"It's not like he needs to take over the world today, the club knows that, the coach knows that and the team knows that."
The teenager burst on to the scene last season, scoring in his Premier League, Europa League and senior international debuts, leading to a call-up for England for the 2016 European Championship in France.
Ibrahimovic said too much pressure on Rashford's shoulders could have an adverse effect on his progress.
"There is no need to rush to push him and put him in the heat zone and put a lot of pressure on him because that can have the opposite effect," he said.
"Time by time, he will take over everything. It's about having patience."
Manchester United travel to Feyenoord in the Europa League on Thursday.
(Reporting by Nivedita Shankar in Bengaluru; Editing by Clare Fallon)
