Barbarians hooker Schalk Brits has been cited for punching Saracens team-mate Owen Farrell during Saturday's clash with the British and Irish Lions in Hong Kong.
Brits will appear in front of an independent disciplinary panel on Sunday following the first-half incident.
Farrell was originally penalised by referee Steve Walsh for retaliating but Walsh reversed his decision on viewing television replays and showed Brits a yellow card.
Lions coach Warren Gatland has warned Farrell about the need for strict discipline after a flare-up.
"It was just a ruck situation. Owen is holding on to his jersey, Brits has got a bit frustrated and let fly," said Gatland.
"The good thing was that Owen wasn't injured or knocked out.
"I was pleased he (Brits) wasn't sent off, and just given a yellow card. Had they played with 14 men it would have been less of a hit-out for us.
"Sometimes it is hard when someone lays a punch squarely on the side of your jaw not to react. But we strongly want to keep discipline and sometimes you have to take one for the team. You can't retaliate.
"We are going to emphasise from the start of this tour the importance of keeping our discipline."
Meanwhile Barbarians coach Dai Young tried to lay to rest the on-off selection saga of Hong Kong's only representative in his squad, Rowan Varty.
Varty was left out of the initial matchday squad, then announced as an unorthodox extra replacement a few hours later, with the Barbarians saying he was cover for Mike Tindall, who had picked up a slight injury.
However, Varty did not make the final team-sheet and missed out on the chance to play in front of his home fans at Hong Kong Stadium, with Tindall taking the field instead.
"There was no on-off about it," Young told reporters. "He was always our 24th man so when Mike Tindall had a niggle he was put on standby.
"Mike was fit in the end. But Rowan didn't look out of place in the squad and I am sure he has got a big future ahead of him."