Tommy O'Donnell is likely to miss Ireland's autumn Test opener against South Africa after suffering a shoulder injury.

The Munster flanker was due to undergo scans on Tuesday on a problem suffered in training on Monday.

Ireland host the Springboks in Dublin on Saturday, and could well do so without O'Donnell's fellow back-rowers Jack Conan and Dan Leavy.

Those absentees could now pave the way for Rhys Ruddock to take a seat on the bench, with British and Irish Lions trio Sean O'Brien, CJ Stander and Peter O'Mahony a potential starting back-row.

"Tommy O'Donnell picked up a bit of a shoulder bump in training yesterday so he's due to have a scan at some point today," said Ireland forwards coach Simon Easterby.

"Jack Conan sat out training, he just had a heavy workload.

"Dan Leavy had a bit of tightness in his hamstring, obviously he played at the weekend. Again it's just managing his workload.

"It's just about being sensible and earmarking players who may have potential weaknesses.

"If you know about things, at least you can prepare for that and not take any unnecessary risks."

Connacht's New Zealand-born centre Bundee Aki is primed for his Test debut for Ireland at the weekend, and several columnists, including Neil Francis on Monday's Claire Byrne Live, have hit out at World Rugby's residency qualification rules.

Easterby insists Aki will be unflustered by any such discussions however, with the 27-year-old likely to reprise his old Connacht centre pairing with Robbie Henshaw.

"The rules are the rules and Bundee has invested time into moving to Connacht and has played exceptionally well while playing here," said Easterby.

"There is always the question over eligibility of players, whether it's residency, grand-parentage, parentage if players aren't born in the country. That will continue.

"Bundee and other players will be potentially singled out but he's certainly fitted in well and has trained well. We're really happy with what he's already shown in terms of his training.

"I'd say he wouldn't be listening to, or privy to that criticism.

"He's a confident character, you've seen him play. A lot of you would have met him, he's confident in his ability.

"He wouldn't have put himself in this position had he not had the confidence in himself and in the group that they back him in that decision. He's not the first and he won't be the last player to do it."

Injuries to Garry Ringrose and Jared Payne open the door for Henshaw to move out to 13 to accommodate Aki at inside centre, with Easterby admitting Ireland will be forging new pairings across this autumn.

"It's a chance to see some combinations; we haven't been together as a group in terms of the Lions players and a few others through injury," said Easterby.

"This series is a chance to look at some of those combinations, and 12 and 13 being one of them with Jared and Garry being out injured." 

Ireland v South Africa (5.30pm kick-off), live on RTÉ 2 and the RTÉ Player from 4.30pm & on RTÉ Radio 1's Saturday Sport, with a live blog on RTÉ Online from 4.30pm.