The Portuguese forward currently earns around £385,000 per week at Old Trafford, following his remarkable return to the club from Juventus last summer.
However, according to The Athletic, that wage could fall to below £300,000 per week this summer should United fail to qualify for next season's Champions League.
Therefore, with the Red Devils still in the knockout stages of this year's competition, that could prove another route for the club to qualify should they fail to break into the top four in the Premier League.
United currently sit seventh in the table ahead of Saturday's visit of West Ham United, with two points separating them from their opponents in fourth spot.
Meanwhile, Ronaldo has scored 14 goals in his 23 appearances so far this season, but has cut a frustrated figure of late, particularly in his substitution during the second half of United's 3-1 victory at Brentford on Wednesday night.