A track-suited O'Callaghan was seen later limping through Clermont with an ice bag strapped to his leg surrounded by his teammates in their Magee number ones (suit, shirt and tie) but after yesterday's lay-off it was back to business again today as he took a full part in training at Musgrave Park.
" I'm fine, not a bother," he said, after a session in which he showed no signs of any discomfort.
Looking back on last Sunday's game, it was he said, "a massively physical game. It was so fast, particularly in the opening half when they just seemed to be coming at us from every angle. I suppose we didn't do ourselves any favours the way we coughed up ball but in fairness to them that came about because of the pressure they put on us."
At half time and trailing 20-6 what was the attitude and what was said in the Munster dressing room. " Well we were glad to get in there and collect ourselves. Circle the wagons if you like. There was no ranting or raving by anyone, there never is. We spoke about getting our hands on the ball and holding onto it. Try and build the phases, give our backs something to play with. We knew we had to front up, up front and we knew we couldn't let them get another try."
"We said we had to get the first score in the second half but as it turned out they did (a penalty) but we were starting to motor by then and Mafs' try came shortly after that. It was so important an gave us a great lift."
Now facing into the match that will decide their future in this year's competition, O'Callaghan and his colleagues will focus on what they must do rather than worry about how Wasps will play. "They're the champions. A really good side. They're top of the Pool and they hold the whip-hand. I don't think coming to Limerick will bother them at all. They came to Dublin 2004, played in front of a huge Munster support and won. So they'll feel they can do it again.
"But for me, it's a case of looking to my own game, concentrating on that and nothing else. The same goes for the rest of the lads. Yes, we will spend a deal of time looking at the videos of their games. Looking back on the game in the Ricoh, see what areas can be be improved.
"Just as importantly will be looking at their more recent games because things will have changed from the Ricoh. That was early days, their lads just back from the World Cup and they'll have improved from then.
"But hopefully so have we. I think it's going to be a great occasion. It seems we always have these sort of games to wind up the Pool stages, Leicester last year, Gloucester and Sale before that."
" I suppose it makes for a great day our for our supporters."
"And of course our supporters will play a part. A huge part. But we know and just as importantly, they (Wasps) know, as Rog and Axel have said, its what we do or don't do that will decide this one."