Joining Barcelona has been Rashford’s preferred option since he declared in December that he was ready for a new challenge after being dropped by United head coach Ruben Amorim.
The move will be Rashford’s second consecutive loan spell after a six-month stint with Aston Villa in the second half of last season.
The forward is expected to complete a medical with the La Liga club early this week, with the aim of being able to join Barcelona’s pre-season tour of Japan and South Korea on Thursday.
Should Rashford join the tour, he could come up against former United team-mate Jesse Lingard.
Lingard, 32, is in his second season with K League side FC Seoul, who face Barcelona on 31 July.
Another of Rashford’s former team-mates, Monaco midfielder Paul Pogba, told YouTuber IShowSpeed: “I’m happy for him because they (United) took his number.
“Manchester United are losing a great player. Unlucky for them. It’s great for Barcelona.
‘It’s not really his (Amorim’s) fault. If he doesn’t believe in someone… He needs to win. If he doesn’t win they’re going to sack him.”