Connacht fly-half AJ MacGinty has been ruled out for four weeks, handing the PRO12 leaders a playmaking injury headache.
MacGinty started last weekend's 7-6 defeat of Leinster but limped off with a shoulder injury, becoming the third Connacht No.10 to be sidelined.
The Irish region confirmed on Tuesday that the U.S. international would be out for "at least four weeks" and with Jack Carty and Craig Ronaldson also on the treatment table, the league leaders appear short on options ahead of their trip to Ulster on Friday night.
There was better news on Ireland forward Ultan Dillane, who could return from the shoulder knock that ruled him out against Leinster, while a decision on the fitness of Jake Heenan will made ahead of Wednesday's team announcement.
Ulster hope to welcome back Ireland trio Rory Best, Andrew Trimble, and Jared Payne for Friday's match but Alan O'Connor is definitely out and Nick Williams remains a serious doubt.