Rojo will be confirmed as a United player this week pending a successful medical.
United will pay an initial fee of €10m and two separate instalments of €5m in December 2014 and July 2015.
There is also a clause within the contract meaning Sporting will receive 20% of any deal if Rojo was to be sold for in excess of €23m in the future.
Nani going back on loan to the club from which he joined United is another chance for him to reboot his career and fulfil on the promise which he had but has lost since his injuries over the past two seasons.
#mufc has reached agreement with Sporting Lisbon to sign defender Marcos Rojo, subject to a medical and personal terms.
— Manchester United (@ManUtd) August 19, 2014