Giovanni van Bronckhorst’s side have one foot in the quarter-final after sweeping past Red Star Belgrade at Ibrox.
The first-leg of the tie saw Rangers run out 3-0 winners, taking a big advantage to Serbia next week.
Of the 16 teams left in the tournament, the Scottish champions are sixth favourites with their odds slashed from 25/1 before the match on Thursday to just 14/1.
At the start of the group stages they were 150/1.
They are behind Barcelona, RB Leipzig and Sevilla.
Betfair spokesperson Sam Rosbottom said: “Another famous European night in Glasgow saw Rangers take a huge step in booking their place in the Europa League quarter-finals by easing past Red Star Belgrade. Giovanni van Bronckhorst’s men have moved from 25/1 to 14/1 to win the tournament overnight, while Barcelona remain the 5/2 favourites to go all the way.”