Giovanni van Bronckhorst’s men trail 2-0 from the first leg in Belgium against a side who had the best away record in the Jupiler League last season, losing just once in 17 games during the regular campaign.
Encouragingly for Rangers, Union SG lost on the road on Saturday, going 3-0 at Mechelen.
Tuesday at a packed Ibrox is likely going to be different but former Celtic and Scotland star Kris Commons has backed the Europa League finalists to find their way into the Champions League play-off where the opposition will be either Monaco or PSV Eindhoven.
However, the Daily Mail pundit has explained what Rangers require to ensure they get the scoreline which will take them through.
"It's all about how Rangers start,” he wrote in his column. “The atmosphere will be electric and they have to feed off that and keep the fans with them.
"The Belgians won't have experienced anything like it. Far better teams than them have been intimidated by the atmosphere that the big clubs in Glasgow can generate on nights like these.
"If Rangers score in the first 30 minutes, I think the momentum will turn and they'll get through with something to spare. It's a matter of unsettling Union from the very first minute.
"You want to get them facing their own goal and remain under pressure. If they concede early, I could see them crumbling.”
Key to Rangers’ success will be Alfredo Morelos.
The Colombian was back from injury on Saturday, his first appearance since March, scoring in the 2-0 win over Kilmarnock.
He came off the bench at the weekend but he could be handed a start on Tuesday.
"After so long out, it's going to take him a few matches to get fully up to speed but his mere presence tomorrow is a huge boost.” Commons said.
"It's not just his goal record. His physicality poses different problems to their defenders. He's a handful. He'll wind them up and push them about. They won't be looking forward to facing him."