One of Geoffrey Rush's co-stars has told a Sydney court he saw the actor cup the bottom of actress Eryn Jean Norvill's breast during a performance of King Lear.

Key points: Actor Mark Winter said he saw Mr Rush make "a boob squeezing gesture" above Ms Norvill

Actor Mark Winter said he saw Mr Rush make "a boob squeezing gesture" above Ms Norvill He said Mr Rush cupping Ms Norvill's breast during a scene was not typical

He said Mr Rush cupping Ms Norvill's breast during a scene was not typical Mr Winter said he was friends with both actors

Actor Mark Winter, who played Edgar during the Sydney Theatre Company (STC) production in 2015-16, gave evidence in Mr Rush's defamation case against Nationwide News.

Mr Rush is suing the company, which publishes The Daily Telegraph newspaper, and one of its journalists Jonathan Moran over articles printed late last year that claimed he behaved inappropriately towards a younger female colleague during the production.

That colleague was subsequently revealed in legal proceedings as Ms Norvill.

"I can say unequivocally that his hand touched her breast," Mr Winter told the court while being cross-examined by Mr Rush's barrister Bruce McClintock SC.

Mr Winter said during the final scene of King Lear, Mr Rush would usually touch Ms Norvill's "shoulders, hair, face, body and side" and would lift her up into a cradling position.

But he said one night, Mr Rush did something different from what had been rehearsed.

"On that occasion I saw Geoffrey's hand cupping around the bottom of the breast, which was something I hadn't seen on stage," he said.

"The nipple was not covered, it was sort of more a cupped position, the side and under, but not like a squeeze."

Mr Winter said he thought Mr Rush had his hand on her left breast for about five seconds.

"It was long enough for me to have a series of thoughts that took me outside the action of the play," he said.

Geoffrey Rush (L) arrives at court with director Fred Schepisi. ( AAP: Dean Lewins )

Mr Winter also said in a different instance he saw Mr Rush performing a "Three Stooges style skit" while kneeling over Ms Norvill, who was lying on the floor, and heard others in the cast laughing.

"It was a sequence of quick jokes ... and joke gesture at the end," Mr Winter said.

"A boob squeezing gesture.

"They were in the final moments of the play."

"I know that people laughed at the time ... I tuned in late. That's all I can say about that."

Mr Winter said both Ms Norvill and Mr Rush were his friends and that he had studied and performed with Ms Norvill numerous times.

He also said Mr Rush had given him a reference after the production of King Lear.

He described Mr Rush as "a respected figure and a friend".

The trial continues.