The Welshman did not train with the rest of the Real squad on Tuesday after picking up the injury in training a fortnight ago.
Bale - who moved to the Bernabeu from Tottenham for a world-record fee in the close-season - struggled with back and thigh problems earlier in the season, but has notched seven times in 10 La Liga appearances in a promising start to his career in Spain.
Real returned to training on Sunday following time off for the mid-season break, but Bale had to train alone.
Centre-back Raphael Varane is also unavailable for selection on Thursday, with the Frenchman continuing to suffer with a knee injury.
Carlo Ancelotti's side return to Liga action against Celta Vigo on Monday.
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
