Nuno said Valencia want to bring in cover for Nicolas Otamendi, after Manchester City ruled out loaning the La Liga club Eliaquim Mangala.
Valencia coach Nuno hailed the departed Nicolas Otamendi, and said he was still chasing a replacement for the new Manchester City centre-back.
Otamendi's City move was secured on Thursday, and while central defender Eliaquim Mangala was ruled out of a loan move from City to Valencia by Manuel Pellegrini, Nuno was still hopeful of bringing in cover.
Valencia are preparing for their La Liga opener away at Rayo Vallecano, just days after winning the first leg of a UEFA Champions League play-off against Monaco 3-1.
"We have the feeling that we need one more centre-back," said Nuno, who played Shkodran Mustafi and Ruben Vezo as his central pairing against Monaco.
"But we still have a few days, and the important thing is that for tomorrow and next Tuesday we have two great centre-backs, a quality defence and we are confident in that sense.
"Mustafi and Vezo's great performances against Monaco guarantee us that tomorrow they can do the same."
Otamendi made 35 league appearances for Valencia, the defender scoring six La Liga goals, and Nuno wished the Argentine well in the Premier League.
"I read Nico's statement. From this club we wish him all the best and a lot of success in this new stage," Nuno said.
"I have a great admiration for him because while he was here he always gave the maximum as a professional."
Valencia's trip to the Campo de Futbol de Vallecas holds no fears for Nuno's men.
Valencia have lost just once on the road at Rayo since the latter's promotion for the 2011-12 La Liga season, winning three times twice there - plus a Copa del Rey triumph in December.
"Vallecas is a difficult ground," Nuno added.
"Rayo is a team very well managed, organised team and always difficult to beat. But we are motivated to go there and compete."