Brian McLaughlin's men face Glasgow Warriors at Ravenhill on Friday but they may be forced to do so without two of their most high-profile players.
Paddy Wallace and Stephen Ferris picked up lower leg injuries during Ireland's win over South Africa on Saturday and both are now doubtful for Ulster's penultimate Magners League match of the year.
Inside centre Wallace limped off after just 23 minutes of the nail-biting encounter between the reigning Six Nations Champions and the current World Champions in Dublin.
The 30-year-old needed assistance from two support staff as he left the field without placing any weight on his right side.
Blindside flanker Ferris lasted longer than his provincial team-mate in the final Test of Ireland's three-match autumn series but his afternoon came to an end halfway through the historic 15-10 triumph.
Having been injured earlier on in the first period, Ferris played on until the interval but failed to reappear after the break.
Ireland coach Declan Kidney was unable to give any indication of how long the pair will be out of action for but an announcement is likely to be made in the next 48 hours or so once further medical assessments have taken place.
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