Wallabies star Kurtley Beale has been accused of punching his teammate Cooper Vuna following the Melbourne Rebels' record 64-7 Super Rugby loss in South Africa on Saturday.
Hours after the Rebels' record 10-try defeat by the Coastal Sharks in Durban, Vuna alleged in a tweet that Beale hit him.
"I need to leave right now, this ain't for me! I tried to help someone but got punched so instead of putting him in hospital il leave!" Vuna posted.
The tweet was deleted but later published on a fan website with one Twitter user asking Vuna if his alleged assailant was drunk.
Vuna replied: "Hmmmmm his name is kurtley_beale bloody grub!"
Beale did not play in the Durban match as he continues his recovery from hand surgery, while the Sharks game was Vuna's first competition match this season after a shoulder injury.
Rebels media manager Adam Freier issued a statement on Sunday but indicated the club would not name the players involved until it had been dealt with.
He said no outside parties were involved.
"The Melbourne Rebels would like to respond to reports of an incident between players following the team's bus trip home to their hotel in Umhlanga," the statement said.
"The club is treating this matter as serious and a full internal investigation has begun with the players involved.
"Therefore, the club cannot provide any further comment until the internal investigation is completed."
Beale was granted bail last July to attend mediation after appearing in court charged with common assault.
He was allegedly involved in an altercation with a security guard after he and Wallabies team-mate Quade Cooper were refused entry to a Brisbane pub before Australia's first Test with Wales in June.
Beale is expected to undertake his first session of mediation next month.