
Rangers visit Macedonian champions Zeta Golubovci for a second round return leg on Tuesday with a 2-0 cushion. The next day, Red Star are at Estonia's Levadia Tallinn holding a slim 1-0 advantage.
Red Star were European champions in 1991, beating Rangers in the second round of that competition.
"Life has some rules and we must accept them," said Red Star coach Bosko Djurovski after last Friday's draw. "(But) First at all, Red Star must eliminate Levadia and after that we can speak about potential opponents."
Rangers boss Walter Smith agreed: "First and foremost we have to concentrate on getting through against Zeta," Smith told the UEFA website.
"It looks as though Red Star are the favourites to progress in the other tie although they are only one goal ahead from the first leg so you never know what can happen. They are a club with a proud history."
Scotland striker Kris Boyd is an injury doubt for Rangers as they travel to Macedonia. Defender Alan Hutton is suspended after being dismissed for a second bookable offence last week.
Smith was mainly happy last week that Rangers "didn't concede an away goal," saying "the home leg can be the more awkward." Confidence was further raised on Saturday when Rangers won their league opener 3-0 at Inverness.
Red Star are not the only former champions playing this week, as the 1986 winners Steaua Bucharest lead Poland's Lubin 1-0 ahead of their Wednesday meeting in Romania.
The winner should next meet Belarussian side Bate Borisov, who host Iceland's FH Hafnarfjordur with a 3-1 advantage.
Giovanni Trapattoni's Red Bull Salzburg, meanwhile, hold the biggest advantage in the 14 ties, having won 3-0 at Latvian side Ventspils thanks to a hat-trick by Rene Aufhauser.
"Nothing should happen to you if you win 3-0 on the road. But we will be fully concentrated and hope to score a goal or two before half time. Then we will have clinched a place in the next round," said Aufhauser.
DPA