The two clubs and the player have agreed a deal for the 30-year-old to join Middlesbrough on loan for the season, and Negredo will officially sign for Boro if he passes his medical.
The loan deal will include an option for Boro to buy, should the Spain international impress at the Riverside.
Negredo has struggled to find his best form at Valencia, scoring 18 goals in 74 games for the Spanish side.
However, the striker did enjoy a successful spell in England previously, scoring 23 goals in his only season in English football while at Manchester City.