Javier "Chicharito" Hernandez is "now a Bayer Leverkusen player," his agent said after the Mexican striker completed a medical on Monday.
Hernandez, 27, has struggled for game time at United and spent last season on loan at Real Madrid, with Los Blancos opting not to make the move permanent despite a late return to form.
But the Mexico international has been given an opportunity by Leverkusen, who had money to spend following the sale of Son Heung-Min to Tottenham last week.
Agent Eduardo Hernandez told ESPN Mexico: "Javier did the examinations today. He already passed them. He is now a Bayer Leverkusen player."
There was no official confirmation from the clubs as the German transfer deadline passed on Monday.
Hernandez -- believed to be costing Leverkusen around €12 million -- told Sky Sport Deutschland that he is "very happy" before undergoing his assessment in Germany.
#chicharito: "i am very happy!" @bayer04fussball @SkySportNewsHD #deadlineday #fix #skytransfer #ssnhd
- Inga Ortmann (@OrtInga) August 31, 2015
Hernandez has been limited to just three brief appearances as a substitute by United in the opening stages of the new campaign.
And the striker, who failed to convert a penalty during last week's 4-0 Champions League playoff defeat of Club Brugge, did not make the United squad for Sunday's 2-1 loss to Swansea.