Ronaldo recently missed two games with a hamstring problem but returned to action in Wednesday's Champions League game against Lyon.
Race against time: Ronaldo is doubtful for the first leg against Tottenham
He also started Saturday night's derby against Atletico Madrid, playing around 70 minutes in both matches before being replaced.
The ?80million man complained of pain in his left thigh following the derby and he underwent medical tests, where the extent of the damage was confirmed.
According to a statement on the Madrid website, Ronaldo is now likely to be absent for 'between two to three weeks, depending on his progress'.
Fresh blow: Ronaldo featured in Real's 2-1 win over rivals Atletico on Saturday
Ronaldo is now set to miss Portugal's upcoming friendlies against Chile and Finland, and it remains to be seen if he will be fit for Madrid's league match against Sporting Gijon in a fortnight's time and the Champions League clash with Tottenham on April 5.
Nine-times European champions Madrid reached the last eight of the Champions League for the first time in seven years after knocking out Lyon in midweek.
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Source: Daily Mail
Source: Daily Mail