The 24-year-old has scored 93 goals in 297 appearances for the Red Devils since making his debut in 2015 but he has become increasingly disillusioned at Old Trafford.
But Rooney wants the England forward to stay at Manchester United and focus on beating his all-time record of 253 goals.
Rooney told The Sun: "To get the record and be United's highest goal scorer is f***ing massive.
"What I hope is that Marcus Rashford f***ing gets his head out of his a*** and goes and breaks that record. He is a Manchester lad."
Rashford has fallen out of favour in recent months at Old Trafford, starting just three league matches since the turn of the year.
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