Borussia Dortmund have set a 10 August deadline to agree a deal for forward Jadon Sancho - who is Manchester United's top summer transfer target - to leave the club.
The German club have told United they want in excess of £100m for the 20-year-old England winger.
There is no agreement yet on a fee, which would be paid in instalments.
Dortmund have set the deadline because they want undisturbed preparation for the 2020-21 Bundesliga season.
The new campaign starts on 18 September, with the transfer deadline for international deals on 5 October.
Sancho has been at Dortmund for three years, having signed from Manchester City in August 2017 for a fee of about £10m.
In July, Dortmund beat United to the signing of 17-year-old English midfielder Jude Bellingham from Birmingham City in a deal that could be worth over £30m.
They also bought Norway forward Erling Braut Haaland from Red Bull Salzburg earlier in the season - another player United tried hard to bring to Old Trafford.