Valencia say a supporter died after their game with Barcelona at the Mestalla on Saturday.
Reports from Spain claim the fan collapsed after he celebrated Valencia's equaliser.
Santi Mina scored in the 86th minute to earn a point against the La Liga leaders in front of 55,000 fans.
It was Valencia's first game since they appointed ex-Manchester United and England defender Gary Neville as their new head coach.
Neville watched from the stand as his new side drew for the second time in three matches.
Following the game, the Spanish side released a statement saying: "Valencia were sad to learn of the death of a fan following the match at Mestalla on Saturday.
"The club wishes to extend its deepest condolences to the family and loved ones of the deceased."