Grealish, 21, was also suspended by the Championship club for Saturday's draw with Newcastle but will be available for Tuesday's trip to Barnsley.
Police were called to a Birmingham hotel last Sunday morning as guests complained of a rowdy party, which Grealish is reported to have attended.
No arrests were made and Grealish was not among the people thrown out.
"We've fined the boy and he was suspended for today," said Villa boss Roberto di Matteo.
"It's not the first time but he needs to learn from the past and the only one who can do that is himself. He needs to make the right decisions.
"He's 21 now and needs to understand what kind of career he has ahead of him. As long as he does what he's supposed to do we will treat him like everyone else."
Villa's 1-1 draw with Newcastle extended the club's winless run to six games and left them 17th in the early Championship table, with nine points from their opening nine league games.
Subscribe to the BBC Sport newsletter to get our pick of news, features and video sent to your inbox.
Aston Villa have fined Jack Grealish following a club investigation into the winger's part in an all-night party.