Manchester United signed Netherlands cente back Matthijs de Ligt and Morocco full back Noussair Mazraoui from Bayern Munich on Tuesday.
The 25-year-old De Ligt agreed to a five-year deal, with the option to extend for a further year.
The 26-year-old Mazraoui, who can play as a right back or left back, has a contract until June 2028, also with the option to extend for a further year.
No transfer fees were announced but British media reported United was paying £60 million ($77 million) for Mazraoui and De Ligt.
United earlier Tuesday sold Aaron Wan-Bissaka to Premier League rival West Ham for a reported fee of £15 million ($19 million) to end a five-year spell at United.
One of the best one-on-one defenders in the English game, Wan-Bissaka will compete with Vladimir Coufal for the right-back spot at West Ham. Wan-Bissaka returns to London, having started his career at Crystal Palace.
It completes a huge shake-up of United’s defense, with the club having already bolstered its back line in this transfer window by signing 18-year-old center back Leny Yoro from Lille for £62 million ($68 million).