Madrid, Spain (SportsNetwork.com) - Atletico Madrid midfielder Koke could miss up to a month because of a hamstring injury sustained in his team's 4-0 thrashing of Real Madrid on Saturday.

The 23-year-old lasted only 10 minutes before he was replaced by Saul, and tests have revealed on Monday that he suffered a hamstring strain, which puts his status for Atletico's Champions League round of 16 first-leg match with Bayer Leverkusen in question.

Atletico didn't reveal an exact timetable for Koke's return, but the injury will likely keep him out of league matches with Celta Vigo and Almeria as well as a potential clash with top-five side Sevilla.

The Spain international is a key playmaker in Atletico's midfield having scored one goal with eight assists in 20 La Liga matches this term.