Ismaila Sarr would not be eligible to represent Manchester United in the group stages of this season's Champions League if the attacker moves to Old Trafford before October 16.
The international transfer window closed on Monday, but Premier League clubs can still sign players from EFL teams until the end of next week, and it has been reported that Watford would be open to allowing Sarr to move to Ole Gunnar Solskjaer's side for the right price.
However, as reported by The Mirror, UEFA set a deadline of midnight on October 6 for clubs to confirm their 25-man squads for the group stage of the competition, meaning that Sarr would have to wait until 2021 to potentially represent United in the latter stages of the tournament, should they qualify.
The 22-year-old, who has also been linked with Liverpool, scored five times and registered six assists in 28 Premier League appearances for Watford during the 2019-20 campaign.
The Hornets are believed to value the former Rennes attacker in the region of £45m.