Indeed, both players are out for the remainder of the season. They will undergo surgery this week.
Head coach Brian McLaughlin said that Wallace and Trimble are looking at lay-offs of 'six weeks minimum, but it's likely to be longer.'
South African prop BJ Botha sustained a knee injury against Leinster last Saturday and is unlikely to feature against Connacht, despite being named in the preliminary squad.
But fellow front rower Tom Court could be available again. He is due to be assessed after suffering a 'mild concussion' which kept him out of the Leinster game.
Ulster's defeat in Dublin brought their six-match unbeaten run in the Magners League to an end and leaves them still searching for a first success over Irish opposition this season.
The eight-point loss also means they must now win their two remaining games to guarantee a semi-final spot. They are now third in the league table, sandwiched between Leinster and the Ospreys.
McLaughlin added: "We have to win the last two games, no doubt about that. The most important thing for us is to make sure that on Friday night at Ravenhill against Connacht we get the result we need. We're not looking any further than that.
"The first 15 minutes (against Leinster) we were just completely off the mark. What was disappointing was that we went from what was one of our best defensive displays of the season (against Northampton Saints) to possibly our worst.
"We rested up well and we felt we were in a good place. But we didn't play to our potential in any way, shape or form."
ULSTER Squad (v Connacht) - Backs (14): Ruan Pienaar, Paul Marshall, Ian Humphreys, Niall O'Connor, Ian Whitten, Nevin Spence, Darren Cave, Mark McCrea, Simon Danielli, Tommy Seymour, Craig Gilroy, Conor Gaston, Jamie Smith, Adam D'Arcy.
Forwards (18): Jerry Cronin, Tom Court, BJ Botha, Paddy McAllister, Bryan Young, Rory Best, Nigel Brady, Andi Kyriacou, Ryan Caldwell, Dan Tuohy, Johann Muller, Neil McComb, Tim Barker, Pedrie Wannenburg, Thomas Anderson, Willie Faloon, Chris Henry, Robbie Diack.