Asked about the 'walking wounded' O'Sullivan was happy to report that things were looking up in that regard.
" Things look good for everybody at the moment, Shane Horgan took part in quite a bit of this morning's session, John Kelly the same. They're pretty much back to full fitness.
" John Hayes has made good progress, he's running again now. Again we're being careful with him but when we get to landfall in Australia he should be up and running.
" In terms of recovery he is the guy who is furthest back, let's put it that way, but he's going well in his rehab and he's made great progress. We're playing safe because we want to make sure that he's right before we put him back into it. We expect he should get back into it when we get to Australia.
"We'll proceed with caution with John but we're confident he'll be good to go when we get to Australia. That's when the real business starts".
Asked about the most recent call-up to the squad - Paddy Wallace - O'Sullivan predicted an exciting period for the young Ulsterman in the upcoming competition.
"Paddy's hit the ground running but then he's been involved in the squad on an on-going basis. He knows the lie of the land. He really just slotted in.
" It was pretty gut-wrenching on Monday when Jonny Bell went down. It was pretty much close to the end of the session but when he went down everyone knew he was in trouble. It was very sad for everyone to say goodbye to him. The guy himself was devastated and our heart goes out to him. But Paddy came in, he was in Bilbao for that reason, in case anything happened to Jonny and now he's in situe and he's fitted in as you'd expect him to.
" He's pretty much an all-round footballer. We've seen that with him playing full-back for Ulster, and he's played fly-half for them. He's a very good attacking footballer. He takes the ball to the line, he runs good lines himself and has exceptionally good hands off both right and left. He's prettty much a complete footballer.
" The only thing working against him is his lack of experience. But he's got a confidence about his game that we see when he's running with the ball in hand and he's got a kicking game as well. Jonny Bell is a loss but Paddy's a very good guy to have in the squad as cover. And if things go his way in the World Cup he might shine there but I don't want to put any pressure on him because as I've said his experience is limited.
" But he does have the potential to be a very very good international. And maybe now he may have to fulfill that potential sooner rather than later now that he's in the squad."