Ireland wing Andrew Trimble will undergo another scan on his ankle injury after a first look proved inconclusive.
The Ulsterman had a strong outing in Ireland's victory over Wales on Saturday, setting up a try for Keith Earls with a crunching tackle on Wales wing Eli Walker, but he was forced from the field in the first half with an ankle problem.
There is no major concern surround Trimble, but it's unlikely that he will be involved when Ireland play Scotland on Saturday.
Ireland kicking coach Richie Murphy updated the media on the latest injury news today.
Speaking to RTÉ Sport's Michael Corcoran, he said: "Andrew’s injury isn’t simple. He had a scan yesterday and the scan was a little bit inconclusive so he’s going back in tomorrow for another scan and until we see that we don’t really have any further update on him."
Ulster hooker Rob Herring and Leinster centre Noel Reid were released from the World Cup training squad. Ireland must submit a final 31-man squad on 31 August.
Herring's departure leaves hookers Rory Best, Sean Cronin and Richardt Strauss in the squad while even with Reid absent, there are some six potential centres still in the training camp.
Speaking to members of the media, Murphy said: "Two guys have gone back to their provinces this week and over the next while it'll be an ongoing process. Rob Herring has gone back to Ulster and Noel Reid has gone back to Leinster.
"We're not here just to cut players and get rid of them though. We'll see how that is and when we feel we're in a really good position guys will feed back to their clubs."
Tighthead prop Marty Moore and three-quarter Luke Fitzgerald are both fit for selection for Saturday's warm-up Test against Scotland in Dublin. Leinster prop Moore and club-mate Fitzgerald have both now fully recovered from shoulder injuries, with both carrying strong claims to final World Cup selection if fit.
Confirming Cian Healy is still battling his neck problem, Murphy said Ireland will look to mix up selection for Saturday's Scotland visit, following on from last weekend's 35-21 win in Wales.
"Guys are looking good, Marty (Moore) is back in full contact and he looks fine," said Murphy.
"Luke Fitzgerald is back in full contact and looks really good. Most of the squad now are back on their feet and available for selection. There's no real update on Cian Healy, he's progressing well.
"He's not doing full contact but he's doing more or less the whole session yesterday and today.
"He's progressing reasonably well. There will be quite a few changes (to the team to face Scotland). The guys at the weekend did reasonably well.
"It's another opportunity to get more guys onto the pitch over these first two games, so I think you would expect quite a few changes and some guys who haven't had game time will be coming back in."
O'Donnell's dislocated hip has already ruled the Munster flanker out of the World Cup reckoning, and perhaps alleviated the need for another flanker to leave Ireland's squad this week.
"I haven't actually been talking to Tommy myself, but it's a massive blow," said Murphy.
"He had a great performance at the weekend and definitely was right up there fighting for a place in the squad. For anyone at this stage, after putting in a really gruelling five weeks of training, it's tough for him to miss out."
Murphy confirmed Ireland would not add a back-row replacement in the wake of the injury O'Donnell suffered in Cardiff last weekend.
"There's probably no need in that position," said Murphy, when asked if Ireland would boost resources.
"Obviously it's one of those positions that we have a lot of really talented players, so it does open up opportunities for other guys. I don't think we need to look at the squad at the moment."