Ringrose withdrew on the eve of Saturday’s 34-20 Guinness Six Nations success over Italy due to a minor calf injury, while fellow centre McCloskey and wing Lowe sustained similar issues in Rome.
Loosehead prop Cian Healy, who is yet to feature in this year’s championship because of a hamstring problem, also did not take part in the open training session against Ireland’s Under-20 side at the Aviva Stadium in Dublin.
But captain Johnny Sexton, tighthead prop Tadhg Furlong, scrum-half Jamison Gibson-Park and centre Robbie Henshaw were all fully involved ahead of Ireland’s trip to Murrayfield on Sunday, March 12.
Forwards coach Paul O’Connell allayed fears about the absentees.
“I don’t see any problem with those four guys who didn’t train today but we’re just trying to look after them,” he said, according to the42.ie.
Sexton watched the Stadio Olimpico triumph from the stands as he nursed a groin issue sustained in the round-two win over France, while Furlong (calf), Gibson-Park (hamstring) and Henshaw (wrist) have so far been unavailable to head coach Andy Farrell.
Ireland head to Edinburgh seeking to remain in Grand Slam contention on the back of bonus-point victories over Wales, Les Bleus and Italy, with O’Connell encouraged by the potential return of a host of star names.
“They’re all very good players,” he said.
“They speak very well, they generally have a lot of logic to add whenever we have problems to solve.
“It’s been brilliant to go these three games unbeaten without some of those guys, and for them to come back in now hungry, with a bit of a different voice and a different perspective as well.”