Modric and Bale each did gym work indoors as they attempted to recover from injuries sustained playing in the Euro 2020 qualifier between Croatia and Wales on Sunday.
It leaves Madrid uncertain over the fitness of two key players, with the crunch La Liga game against Barca at Camp Nou fast-approaching on October 26.
Wales coach Ryan Giggs said Bale was struggling with pain in his calf towards the end of their draw with Croatia in Cardiff but suggested the problem was cramp.
Madrid confirmed on Tuesday that Modric sustained a thigh injury in the match.
“Following the tests carried out today on our player Luka Modric by the Real Madrid medical department, he has been diagnosed with a bruise in his right quadriceps,” a club statement read. “His recovery will continue to be assessed.”
Real Madrid, who sit top of La Liga, play away at Mallorca on Saturday and at Barcelona a week later, with an important Champions League group game away at Galatasaray in between.
Lucas Vazquez has also picked up a knock and is unlikely to be available this weekend.
