The Spanish international joined Los Che on loan from Manchester City in the summer window, but has not yet featured for the La Liga side after arriving with an injury.
"When I made my announcement, I was convinced that it would happen. I learned that there were moments of tension in the negotiations, but that's normal," Inside Spanish Football quotes Nuno as saying at a press conference.
"What's most important is that he's with us. I see that he's going to be joining us sooner than we thought. We thought he'd be back by the beginning of October but it looks like he'll be back sooner."
Negredo scored an impressive 85 goals in 182 games for Sevilla between 2009 and 2013, including 25 La Liga goals during his last season in Spain.