Spurs have been among the busiest clubs in the market this year, spending more than £200m as manager Roberto De Zerbi reshapes his squad ahead of his first full season in charge.
The club broke its transfer record twice in a matter of days to land midfield duo Sandro Tonali and Mateus Fernandes for £100m and £85m respectively, while Jan Paul van Hecke arrived from Brighton for £52m and Marcos Senesi, Andy Robertson and Martin Dubravka all joined on free transfers.
That spending has been balanced by a string of departures. Luka Vuskovic has joined Brighton for £50m, Radu Dragusin has moved to Fiorentina on loan with an obligation to buy worth around £21m, and striker Alejo Veliz has completed a permanent switch to Bahia.
Yves Bissouma was among 11 players released at the end of their contracts, while loanees Randal Kolo Muani and Joao Palhinha returned to Juventus and Bayern Munich respectively. Thompson follows midfielder Alfie Devine, who completed a permanent £6m move to Preston earlier this month, out of the academy pipeline.
Thompson himself scored 13 goals and provided six assists last season across Under-18 to Under-21 level, including seven goals in as many UEFA Youth League games, and was named in Spurs' first-team matchday squad on three occasions without making his senior debut. He signed his first professional contract with the club in May 2025 but had expressed a desire to relocate for personal family reasons.
Manchester United will pay an initial £4m for the England youth international, with a further £4m available in add-ons tied to first-team achievements, taking the deal's potential value to £8m.
Tottenham have retained matching rights along with a sell-on clause reported to be worth 20% of any future profit. It remains unclear which of United's squads Thompson will join, or whether he will be included in the travelling party for Friday's pre-season fixture against Rosenborg in Norway.
The move underlines United's continued appetite for developing young talent outside the traditional academy pathway, with Thompson having been regarded as one of the most highly-rated prospects to come through Tottenham's youth system in recent years.
Spurs, for their part, are understood to be keen to maximise value from academy sales this summer having felt they fell short of fair market prices for departing graduates in previous windows.