Ulster are hoping Ireland internationals Iain Henderson (knee), Marty Moore (concussion) and especially Darren Cave (ribs) will recover to face Leinster in Saturday's Champions Cup quarter-final at the Aviva stadium but Will Addison (back) and James Hume (ankle) leave the 15 point underdogs short of centres.
Cave is the only remaining specialist 13 as Luke Marshall only recently returned to training.
Addison's back problem denied him an opportunity to feature for Ireland during the Six Nations. The English-born Irish qualified versatile back has been revelation for Ulster this season and represents a major loss.
Henderson trained this afternoon at the Kingspan stadium and while Marcell Coetzee was pulled from media duties, the Springbok flanker is expected to feature this weekend in a backrow alongside Dubliner Jordi Murphy and Sean Reidy.
"It's day by day with [HENDERSON]," said Ulster backs coach Dwayne Peel. "The call will be made later in the week.
“[MOORE] is going through return to play protocols so hopefully he’ll be fine.”
Head coach Dan McFarland must also plan the downfall of the European champions without wingers Louis Ludik (knee) and Craig Gilroy (back).
This indicates the selection of Michael Lowry at fullback, Jacob Stockdale and Robert Baloucoune bringing genuine pace out wide with Cave - if he recovers - partnering Stuart McCloskey in the centre.