Arsenal management are already regretting their release of Yunus Musah.
The 16-year-old signed a two-year deal with Valencia following an impressive campaign for the Gunners' U18s last season.
The player was involved in first team training for Valencia on Tuesday.
AS says Valencia boss Marcelino wanted to see Musah in action first hand, with the Spaniard impressed by what he saw.
They also state that those in charge at the Emirates are disappointed that the youngster has left, believing it is a "serious mistake" to allow him to go.
Musah was initially signed to be a part of Valencia's U19 squad, but has been playing regularly for the reserves since his arrival.