The Slovenian international, who kept eight clean sheets in 13 Champions League games as Atletico reached the final last season, has been sidelined since December after having surgery on a dislocated shoulder.
"Oblak has received the medical all clear at the end of Sunday morning's training session," Atletico said in a statement.
"The Slovenian has been able to fully train with the rest of the group since Wednesday."
Oblak's return is a timely boost with Atletico's defence depleted by injuries to centre-back Diego Godin and right-back Juanfran.