It is said the 29-year-old was seen drinking shots, while laughing gas canisters were spotted in pictures of him with friends.
Agbonlahor has been pushed out of first-team contention and placed on a fitness programme by caretaker boss Eric Black.
A club statement read: "Aston Villa Football Club has today suspended Gabby Agbonlahor pending an internal investigation.
"This is following allegations concerning his conduct at the weekend.
"There will be no further comment from the Club in relation to this matter until the investigation has been completed."
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Agbonlahor's latest misdemeanour, which allegedly took place on Saturday night following Villa's 1-0 defeat at Manchester United, comes just weeks after an investigation into his behaviour during a break in Dubai.
No action was taken over that matter but Black later decided the player's condition was not of the required level and ordered him to follow a personal fitness regime for two weeks.
The matter also brings more fresh turmoil on Villa following their relegation and the shock resignation of two board members yesterday.
On the field, the team have lost their last nine games and have been without a manager since parting company with Remi Garde last month.
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