The device was hurled onto the field of play in the 86th minute of the La Liga clash, causing the evacuation of El Madrigal and play to be suspended for almost 25 minutes.
Upon landing on the pitch, the canister caught fire and subsequently left scorch marks on the grass as smoke billowed out from both ends.
However, club president Fernando Roig refused to suspect home fans in the aftermath of the incident, instead claiming they had been targeted by an outsider.
"Villarreal CF deplores and condemns what happened," he said. "We are convinced that this is a person outside of Villarreal and has specifically come to harm the club.
"They (the authorities) are making all appropriate inquiries and hope to be able to identify as soon as possible the aggressor and will fall on him with the full weight of the law.
"Such acts do not represent the fans of Villarreal. The club wants to apologise ... and want to acknowledge the work of the security forces in the evacuation."
A club statement read: "Villarreal CF wishes to express its sincere rejection of the vandalism which occurred 86 minutes into the match against Celta Vigo at El Madrigal, where an individual threw a canister of tear gas onto the field... causing temporary suspension of the meeting and public evacuation of the stadium.
"Fortunately, there were no injuries to regret, because the evacuation occurred quickly, in an orderly manner and without incident. The club will condemn this event and will utilise all means at their disposal to try and locate the perpetrator of the act."
