Atletico Madrid's Diego Costa has suffered a groin strain, the club said on Sunday, and is set to miss Wednesday's crucial King's Cup quarter-final second leg at Sevilla and next week's Liga game at home to Las Palmas.
Atletico did not state for how long the Brazilian-born Spain striker would be out, although a report in Spanish newspaper Marca said he would be unavailable for 10 days.
Costa was taken off in the second half of Atletico's 1-1 draw at home to Girona on Saturday, which further dented their slim chances of chasing down runaway Liga leaders Barcelona.
Coach Diego Simeone said after the game he had taken the striker off because he had been playing with discomfort.
"After being substituted in the 61st minute of the game against Girona due to muscle discomfort, Diego Costa underwent a scan on Sunday which diagnosed a strain in his adductor muscles," Atletico said in a statement.
"The ... striker's recovery will depend on how the injury develops."
Atletico are second in La Liga and are eight points adrift of Barca, a gap which could be stretched to 11 if the Catalans beat Real Betis on Sunday.
They trail Sevilla 2-1 in the Cup tie after losing the first leg at the Wanda Metropolitano stadium.
Costa, 29, rejoined Atletico from Chelsea in September for 57 million pounds ($79 million) but was only able to play from January after the club's ban on registering new players expired.
He has made five appearances in all competitions, scoring three times and providing one assist, but has only completed 90 minutes once.