His club said that they were “aware” of 27-year-old Mir’s arrest and BBC Sport understands Mir was not present at a training session on Tuesday.
“He is under arrest for alleged sexual assault,” a spokesperson for Spain’s Civil Guard police force told the AFP news agency.
Reports of the player’s arrest had emerged in Spanish media earlier on Tuesday.
In a statement posted on the club’s website, Valencia added: “In relation to the press reports that have appeared regarding the arrest of Valencia CF player Rafa Mir, the Club is aware of said arrest and, in the absence of details about it, for the moment it can only state that it will cooperate in everything that justice may require.”
The striker moved to Wolves from Valencia in 2018, but played only four times for the club.
He joined Sevilla in 2021 following loan spells at Nottingham Forest, Las Palmas and Huesca during his time at Wolves.
Mir returned to Valencia on loan in July.