The visitors were leading 1-0 thanks to Fabian Orellana's goal in the 83rd minute when the object was thrown from the Villarreal section of the crowd and landed in the Celta penalty area.

None of the players were struck, but referee David Fernandez Borbalan quickly suspended the game after fans sitting near where the smoke bomb had landed rushed to the exits covering their mouths and noses.

Numerous Spanish media outlets reported the offending object was a tear gas canister.

However, after the smoke had subsided, both sides returned to the field and a fine free-kick from Nolito sealed a 2-0 win for Celta.

"On behalf of everyone at Villarreal, I condemn what has happened," club president Fernando Roig said at a press conference after the match.

"I think it is someone not connected with Villarreal, an individual who has committed an act of vandalism.

"Someone who has thrown it from the staircase and immediately ran out of the stadium.

"The police are trying to establish who this person is. I hope they are able to identify the person and that the full force of the law falls upon them.

"It is a similar device to those used by the police to disperse crowds."

It is the second time this week that a match in Spain has been blighted by an object thrown from the crowd as Atletico Madrid were fined 600 euros ($820) after Real Madrid's Cristiano Ronaldo was struck on the head by a lighter during their Copa del Rey match on Tuesday.