Sam Burgess says he was only joking when he pretended to not know who his Welsh opponent was ahead of England's loss to Wales.
The former rugby league star tweeted an apology to his opposite number Scott Williams, saying his response to questions at a press conference were "just banter".
The England centre had replied "who's that?" when asked about earlier comments from Williams that Jonathan Joseph was a more challenging opponent than Burgess who is still inexperienced in rugby.
But Burgess overnight tweeted to assure Williams that he did know who he was, and wishing him luck with his recovery from a knee injury which has ended the Welshman's World Cup campaign.
"All the best with the recovery lad...last week was just banter btw, I knew. Was just playing around with a question asked," tweeted Burgess.
Williams responded by saying the remark had been taken "out of context" and wishing Burgess "all the best for the rest of the tournament."
The Wales centre was injured after a late tackle by Brad Barritt and said he was "devastated" to be ruled out of the tournament.
He was one of many Wales players injured in the second half of the game, with Liam Williams ruled out of Friday's match against Fiji with concussion alongside wing Hallam Amos who dislocated his shoulder.