Atletico Madrid have revealed that Koke suffered a thigh injury in his team's 2-0 win at Eibar on Saturday evening.
The Spanish midfielder was replaced just past the hour at the Ipurua, but there were no initial signs of an injury.
Atletico have confirmed that the 23-year-old did suffer a problem, however, which is expected to keep him out until early October.
A official statement from the Spanish club read: "[Koke] underwent an MRI scan at FREMAP Majadahonda clinic on Sunday and showed to have suffered a grade I-II muscle injury to the proximal third of the biceps femoris in his right thigh, pending any further developments."
Koke is expected to miss games against Getafe, Villarreal and Benfica, but is also a doubt for the Madrid derby against Real Madrid on October 4.
