The 28-year-old Wales international had been looking to making a return for Los Blancos in the Madrid derby at Atletico Madrid next weekend having finally recovered from a calf injury.
However, Real Madrid have released a statement on their website to reveal that Bale is now set to be out for a further month because of the latest issue he picked up during training.
It read: "Our player Gareth Bale, who felt some discomfort in his left leg at the end of Thursday's training session, underwent various tests carried out by the Real Madrid Sanitas medical team.
"He has been diagnosed with a strain to the middle third of the adductor longus muscle in his left leg. His recovery will continue to be assessed."