Neil Lennon's men travel to Denmark to face FC Copenhagen, while Portuguese side Braga head to Ibrox on Thurday in the last-32 of the competition.
Celtic, who dropped into the Europa League from the Champions League qualifiers, topped their group which included Lazio, Cluj and Rennes. They even beat the Italian side home and away.
Rangers reached the knockout stages by finishing second ahead of Young Boys and Feyenoord, taking four points off table-topping Porto.
Back in December Celtic were priced at 40/1 to lift the trophy in Gdansk later this year, with their city rivals 66/1.
Yet, despite the Scottish league leader's excellent recent form they have drifted to 50/1 to win the tournament. Rangers, who have lost their way in the Ladbrokes Premiership, are now 80/1 to win, according to BonusCodeBets.co.uk.
The current favourites are Manchester United, despite their poor form under Ole Gunnar Solskjaer with the team seventh in the Premier League. Sevilla, Inter Milan and Arsenal are also amongst the favourites.