According to reports, the 29-year-old was pictured partying in London last Saturday night, the same night Villa were relegated.
Agbonlahor, 29, had been out of the immediate first-team picture having been placed on a fitness programme by caretaker manager Eric Black.
A statement read: “Aston Villa Football Club have today suspended Gabby Agbonlahor pending an internal investigation.
“This is following allegations concerning his conduct at the weekend. ”
This latest Agbonlahor incident 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 on Monday.
Uncertainty over the club’s immediate direction has now increased following the departures of directors David Bernstein and Mervyn King.
The pair had only taken up their boardroom positions in 2016 and both were key figures in the search for a new manager.
Former Leicester boss Nigel Pearson remains the favourite for the position despite the club’s difficulties. David Moyes, Simon Grayson and Steve Bruce are among those also to have been linked.
Agbonlahor’s future at the club is now also unclear. The striker has had spells out of favour this season and scored just one goal during the campaign, against Norwich in February.