The Spain striker is expected to return to La Liga on an initial loan, although Valencia will also be committing to a permanent deal in the future.
Manuel Pellegrini said at the weekend he wanted to keep Negredo, who is currently sidelined after breaking a bone in his foot in pre-season, but neither the injury nor the manager's comments appear likely to prevent a last-minute deal being done.
Negredo scored 23 goals in his first season in England following his move from Sevilla, but the last of those came in January.
The 29-year-old is among five players who either have left, or could be on the way out of, the Etihad before the deadline.
Micah Richards has joined Fiorentina on a season-long loan, while Scott Sinclair is interesting Swansea and Stoke after being told he does not feature in Pellegrini's plans.
Matija Nastasic has been linked with a number of clubs in England and abroad despite his wish to stay and fight for a first-team place, and Palermo are chasing a loan deal for striker John Guidetti.