The South African-born brothers were at the bar to watch the Rugby Championship Tests when an incident occurred in the upstairs Loft about midnight.

Police were called to the scene with reports of a brawl involving up to 15 people, but when they arrived the matter had been dealt with by security staff and everyone had already dispersed.

No one was arrested and no charges were laid.

Ruan Smith was a member of the Brumbies' extended playing squad this season, while Jean-Pierre was not contracted to club. He did sit on the bench as part of the Brumbies' historic victory over the British and Irish Lions.

Brumbies chief executive Andrew Fagan said the club was treating the allegations seriously and he would investigate the matter when he returned from Sydney this week.

"We were made aware of an incident that took place last night that involved some players within the broader Brumbies training squad," Fagan told Fairfax Media on Sunday.

"At the moment I have limited details and we'll now investigate it further.

"We set very high standards within the organisation and within the playing group and it's disappointing to now have to address an issue like this that's been reported to us.

"Nonetheless, we will investigate it in an appropriate, thorough way and until that process is complete it's difficult for me to comment any further."

An ACT Policing spokesperson confirmed they were called to the Duxton about midnight.

"We attended about 12.10am," the spokesman said.

"The initial report was up to 15 people involved with punches and items being thrown, but when we got there they were all dispersed and there was nothing to see so it had all cleared up.

"There was no official complaint made."

The Smith brothers are twins and both props.

Ruan started the season in the Brumbies' Extended Player Squad, outside the top 30 contracted players, but was called into the side following injuries to Ruaidhri Murphy (knee) and Dan Palmer (toe).

He has 10 Super Rugby caps, two of which were for the Western Force.

Jean-Pierre was not contracted with the Brumbies, but was called in as cover when they played the Lions at Canberra Stadium. He sat on the bench, but didn't play.