Kieran Campbell is a big doubt for Ospreys trip

The in-form scrum-half picked up a rib injury in last Friday's Celtic League success over Llanelli and was replaced at half-time by Neil Doak.

Campbell joins a growing injury list with David Humphreys, Tyrone Howe, and Scott Young all on the treatment bench.

The winners of the tie face an away semi-final to the Scarlets or Dragons.

Meanwhile, hopes to be back in time for the trip to Wales on Saturday week.

"I'm hopeful that I will make it," Humphreys told BBC Sport. "I thought I would be fit for last week, but when I started to train, it was not comfortable.

"I will take things easy this week and hopefully will be ready for the Ospreys."

In the last game between the two, the Ospreys edged home 22-21 in January at The Gnoll with Gavin Henson scoring all his side's points.

The Neath-Swansea combination will confirm later this week whether the game will go ahead at St Helen's or The Gnoll.

If Ulster are to hang on to their Celtic Cup title, they will have to do it the hard way, by winning in Wales which they have not done this season.

The final has been confirmed for Saturday, 14 May at a neutral stadium in the home country of one of the finalists.