Dublin - Leinster are investigating claims from Northampton's Springbok prop Brian Mujati that he was subjected to racist abuse during Friday's pre-season friendly at Donnybrook.
The 26-year-old said the racist remarks came from two South Africans, Leinster lock Steven Sykes and prop Heinke van der Merwe, whom Zimbabwe-born Mujati played alongside at South African side the Lions.
"Steven Sykes and Heinke van der Merwe called me a baboon during the scrums," Mujati, capped 12 times by South Africa, wroteon the social networking site, Twitter.
"Racism is still alive and things don't change."
He added: "The guy then tries to shake my hand after the game. Naturally, I tell him to f*** off.
"I wish them all the best with their careers. I was shocked by how blatant they were being and to think I actually thought I knew Heinke from back in the Lions days."
Mujati's comments were subsequently removed from Twitter.
Meanwhile a Leinster statement said they'd initiated a "full internal investigation," adding: "The managements of both teams are in close communication and hopefully the matter will be resolved as soon as possible.
"No further comment will be made at this time until that resolution has been reached."
Ireland's Sunday Independent newspaper said Van der Merwe and Sykes, who deny the racist abuse, were expected to claim they use the word 'bobbejaan' as a trigger call at the scrum in order to gee up the pack and that it comes from their time playing in South Africa. The word translates as baboon.
The Irish Rugby Football Union is in contact with both Leinster and Northampton regarding the matter.
Neither Mujati nor van der Merwe and Sykes are in champions South Africa's squad for next month's World Cup in New Zealand.