The striker has returned to Spain after City allowed him to join the La Liga outfit after just one season at the Etihad Stadium, and Pellegrini has indicated that their FFP and Champions League restrictions resulted in it suiting both parties for Negredo to leave the club.
The 60-year-old told reporters: "The decision for Negredo to go was very important. We have a restriction on the players that we can use in the Champions League.
"Alvaro Negredo was injured. He wasn't going to be on the list. He wanted to go back to Spain. It all starts from the restrictions due to the money we spent."