Rashford was the subject of a loan move from Sky Bet League One side Crewe Alexandra a week before he made his Man Utd debut, claims Collins.
Collins said: “I spoke to Warren Joyce [United U21 coach] earlier in the season about taking him on loan.
“Warren said we couldn't because they needed him for their U21s. A week later he made his debut for the first team and the rest is history."
Rashford made his United debut in the Europa League against FC Midtjylland, scoring twice.