Former South African international Pedrie Wannenburg sustained a groin injury which is responding well to treatment.
Meanwhile, his back row colleague Chris Henry sustained an ankle sprain which is subject to ongoing treatment and reassessment but at this stage he is not ruled out of contention.
Scrum half Paul Marshall continues to receive treatment for the injury to his right elbow sustained in the recent match against Connacht and reassessment is ongoing.
Previewing the semi-final clash with Edinburgh, Ulster attack coach Neil Doak feels that it will come down to who handles the pressure best on the day.
Ulster suffered a setback in their preparations with a defeat to Leinster at Ravenhill - only their second home defeat in 21 games - but Doak believes there are positives to be taken from the match.
"When you look at the previous week, Leinster played Edinbugh and put 50 points on them. So when you consider that we lost 16-8 and pushed them quite hard, it's disappointing but there are promising signs," he said.
"We had a few boys missing and a few others went off injured, and the guys that came in to replace them did a great job.
"We turned over too much ball, particularly in their 22, and that's disappointing. We got ourselves in good positions but make critical errors and you can't do that against the best teams."
Looking ahead to training this week, Doak remarked: "Stevie (Ferris), Rory (Best) and Dan (Tuohy) weren't involved last week so it's important to get them back in and have a good blow out to get rid of the cobwebs.
"We will have a bit of fine-tuning to do and then it will taper off later in the week."
Edinbugh have played some tremendous attacking rugby in this season's Heineken Cup and beat four-time champions Toulouse at the quarter-final stage.
However, they have struggled with their RaboDirect PRO12 campaign, winning just five of their 21 games.
The former Ulster scrum half believes the involvement of so many of their players in Scotland squads is one of the main reasons for their contrasting domestic and European form.
"During the international periods - the World Cup and Six Nations - they have 10 or 11 players who disappear for weeks at a time.
"They have signed some good players to improve their squad depth, but if you take that number of quality players out of the equation, it's going to affect them.
"It is difficult to compete on both fronts unless you have a massive squad. Their position in the PRO12 gives a false account of how good a team they are and if you look at their stats in the Heineken Cup, it will give a better indication of them as a team."
Ulster have registered bonus point wins both home and away against the Scottish outfit this season, but Doak insists that will have no bearing come Saturday evening.
"It's a semi-final of the European Cup so that won't come into it. It will be about who handles the pressure best on the day. It will be about who does the basics well, who defends well, who gets their set piece right."
Doak says a place in the final at Twickenham next month would be a fitting reward for everyone at Ulster Rugby:
"A lot of hard work has gone in over the past two or three years. While the players and coaches get the plaudits, it will be nice for everyone in the organisation if we can make it through.
"Success at senior level will hopefully allow the game at all levels in the province to flourish. It will be a great occasion on Saturday and hopefully we can get the result."