Atletico Madrid midfielder Koke is expected to be sidelined for a month with a hamstring injury.
Koke: Injured his hamstring in their 4-0 Madrid derby win
The Spain international got hurt during Saturday's 4-0 triumph against Real Madrid and tests done on Monday have revealed Koke has a hamstring injury.
A statement from Atletico read: "Koke has undergone test on Monday afternoon after getting hurt in the opening stages of Saturday's derby.
"The results have confirmed a Grade II muscular lesion in his right thigh.
"The Spain international will begin treatment and he will continue to be evaluated."
Atletico have not said how long Koke will be sidelined but the 23-year-old is expected to sit out his team's next three league games, as well as Atletico's Champions League last 16 first leg match at Bayer Leverkusen on February 22.
Koke has scored one goal and set up eight more in 20 league starts for Atletico this season.
Atletico will also be without suspended midfielders Arda Turan and Raul Garcia for Sunday's La Liga game at Celta Vigo.