The Spanish club sacked coach Pako Ayestaran earlier this week after four straight league defeats left them bottom of La Liga.
They beat Alaves 2-1 on Thursday and are away at Leganes, another newly promoted club, on Sunday.
"There's so many new players, we don't know one another very well," said Nani.
Nani, 29, was one of several summer arrivals at Valencia when he joined from Fenerbahce in July.
The Euro 2016 winner with Portugal said the players will work hard to turn things around.
"The situation is not very good but we have so many games to go," Nani told BBC World Service's World Football programme.
"We have quality in the team but we haven't been getting the results.
"Sometimes it seems as though we are going to get the result and then we lose the game.
"I'm very confident we will have better results in the future."
Nani spent eight years at United before leaving for Sporting Lisbon in August 2014.
He helped United win four Premier League titles, one Champions League and two League Cups.
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Valencia's poor start to the season is partly down to the players not knowing one another very well, according to former Manchester United winger Nani.