The footballer felt discomfort in the right hamstring, according to AS.
According to the source, Bale will not take part in the match with Celta in the Spanish Example.
He also risks missing the Champions League group stage first round meeting with Inter Milan.
This season, Bale played three matches in the Spanish Example and scored one goal.
The Welsh striker joined Real Madrid in 2013.
Bale spent last season on loan at Tottenham.
Bale has previously stated that he believes in the success of Cristiano Ronaldo at Manchester United.