Gloucester head coach Johan Ackermann and his son Ruan are the subject of a police investigation following a nightclub altercation that left one man with facial wounds.
The incident was reported in Cheltenham in the early hours of Sunday morning, police said, which was shortly after Zebre had been defeated 69-12 in a Challenge Cup match at Kingsholm.
Former South Africa international Johan Ackermann and his back-row forward son both joined Gloucester ahead of the 2017-18 season.
A family friend of the victim - who has yet to be interviewed - used social media to release details of the alleged assault including photos of the injuries said to have been sustained.
"Gloucestershire Constabulary is investigating a report of an incident which happened at the 21 Club in Regent Street, Cheltenham in the early hours of Sunday morning, 17 December," a police statement read.
"The allegation is that there was an altercation between two groups of men during which one of the men sustained facial injuries.
"The incident was reported just before 1.30am. Police officers arrived shortly afterwards but all those involved had left the scene.
"Investigating officers will be examining CCTV footage this week and speaking to witnesses. No-one has been arrested.
"Anyone with information is asked to call Gloucestershire Constabulary on 101 or email email@example.com quoting incident 51 of 17 December."
Gloucester, who have risen to second in the Aviva Premiership table following a run of five successive victories, are also investigating the alleged incident.
"We're aware of the allegations and we're looking into them. We can't make any further comment at the moment," a club statement read.
Following an erratic start to the campaign typical of the club, their 47-year-old coach has transformed them into title challengers.
After a 57-10 rout at Sale in late September, they have have embarked on a winning run that includes victories over Bath and Saracens.
The form of 21-year-old Ruan Ackermann has been influential in the move up the table and the number eight was named Aviva Premiership player of the month for November.
Johan Ackermann won 13 caps for the Springboks from 1997 to 2007 and as a coach led the Lions to consecutive Super Rugby final appearances, resulting in him being named South African coach of the year in 2014, 2015 and 2016.