ERC has confirmed that an investigation has begun into the circumstances surrounding the blood substitution of Harlequins’ Tom Williams and the subsequent return of outhalf Nick Evans to the field during last Sunday’s Heineken Cup quarter-final clash at The Stoop

ERC Disciplinary Officer Roger O'Connor is carrying out the investigation that will include gathering statements from match officials, the two teams involved and a review of broadcast footage from the game. He will then determine whether any further action is necessary.

New Zealander Evans had been replaced by Chris Malone 10 minutes into the second half, but when Malone sustained a hamstring injury, Harlequins coach Dean Richards replaced the Australian with utility back Williams.

When the latter suffered a “blood injury”, Richards sent Evans back on to the pitch, a move which is within the laws of the game because Malone’s introduction for Evans had been officially noted as a tactical replacement as opposed to one enforced by injury.

Earlier in the week, an ERC spokesperson said: “We are going to look into the process and the protocol to try and protect the integrity of the sport in relation to the replacements issue.”