Gary Neville faces a "very difficult" job reviving Valencia's fortunes, says Manchester United boss Louis van Gaal.
Former United captain Neville, 40, has been appointed head coach until the end of the season, despite having no previous managerial experience.
"Valencia is a very big club in Spain with a lot of history," said Van Gaal.
"They have won a lot of titles also, so it's a big step, a big challenge for him. I am very happy but also curious how he will do."
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Valencia have won La Liga six times but are without a major trophy since winning the Copa del Rey in 2008.
They are ninth in La Liga ahead of Saturday's home game with champions and leaders Barcelona.
Van Gaal had two spells managing in La Liga, both with Barcelona.
The 64-year-old, who won back-to-back domestic titles at the Nou Camp in 1998 and 1999, believes not speaking Spanish is a big hurdle for Neville to overcome, although he has his younger brother, Phil, on the coaching staff to help him.
"He doesn't speak the language so it's very difficult," added Van Gaal.
"He has his brother, he speaks fluent Spanish, but still it's a big challenge and I wish him a lot of luck because he needs luck."
However, asked if the language barrier would prove to be Neville's biggest obstacle to success, Van Gaal said: "No, you have also culture dimensions, that is also difficult to understand."
Neville's first match in charge will come next Wednesday when Valencia host Lyon in the Champions League.
Phil Neville and interim head coach Voro will take charge of Saturday's home game against league leaders Barcelona.