The Spain international was one of the Catalan club's top targets in January, but Celta Vigo refused to let the 29-year-old go
The former Barca B player had been linked with a return to the club for several weeks after showcasing impressive form for Celta Vigo.
Nolito scored seven goals in his first nine league appearances this season, but has missed their last six fixtures with a hamstring problem.
Mestre said the club went all out to land one of Luis Enrique's top targets, but claimed their La Liga rivals would not budge.
"Barcelona put in all they could, plus even more to try to sign him," the 53-year-old said at the Mundo Deportivo gala.
"There were negotiations and we did make offers and alternative deals more than we could.
"But on the other side, Celta did not give in."