According to club sources, the pair are expected to be sidelined for around four weeks but should recover in time for the World Cup, which kicks off in less than 50 days.
Guler's setback came in the final training session before Friday's meeting with Real Betis. Muscle discomfort forced the Turkish midfielder to remain in the gym and skip group work, and subsequent tests diagnosed a muscle injury to the hamstring in his right leg.
Militao's injury was more immediate and more visible. The Brazilian defender felt a twinge in a challenge shortly before halftime in Tuesday's match against Alaves and signalled straight away to be replaced.
While coach Alvaro Arbeloa initially struck an optimistic tone after the game, an MRI scan later revealed a muscle injury to the hamstring in Militao's left leg.
It marks another setback for the Brazilian centreback, who has endured a succession of injuries in recent seasons, including ACL tears in back-to-back years.
With six games left, Barcelona top the LaLiga standings on 82 points, nine ahead of Real on 73. The sides meet in a Spanish Clasico at Camp Nou on May 10th, where Barcelona could seal the title for a second successive season with victory over their old rivals.