Some sports fans say that Villanueva's locker-room tweet may have been a first, the Milwaukee Journal Sentinel reported. Bucks officials called it an "isolated incident" and said it was under investigation.
The game at the Bradley Center was tied 41-41 when Villanueva went to the locker room and used his Twitter utility.
"In da locker room, snuck to post with my twitt. We're playing the Celtics, tie ball game at da half. Coach wants more toughness. I gotta step up," he said.
The Bucks went on to clobber the Celtics 86-77 with Villanueva scoring 19 points and making seven rebounds.
"By the way, lets just get the record straight, my halftime twitt had no interference with what goes on regularly during the locker room," Villanueva tweeted later that night.