Atletico Madrid have received their second coronavirus blow in as many days after striker Moussa Dembele tested positive, following team-mate Joao Felix.
The Liga leaders revealed the French forward, signed from Lyon in the January transfer window, has been forced to self-isolate following a round of routine testing of all club players and staff.
It means that Dembele, along with Felix, is now a doubt for Atletico's Champions League round of 16 first leg clash against Chelsea later this month.
A statement from Atletico read: "Our staff underwent PCR tests yesterday as recommended by La Liga, in addition to the first weekly antigen tests that appear in their protocol, and Moussa Dembele has had a positive result for Covid-19 in the PCR test.
"The forward remains isolated at home in strict compliance with the recommendations of the health authorities and La Liga protocol."
Atletico now have four players in self-isolation - Yannick Carrasco and Mario Hermoso were confirmed to have Covid-19 four days prior to Felix, who tested positive on Wednesday.
Atletico will definitely be without Dembele for their upcoming La Liga fixtures against Celta Vigo and Granada, but he could be out of quarantine by the time they travel to Levante on February 16, although he will only be cleared to play in that fixture after a passing a negative test.
The current Liga leaders are due to play Levante again on February 20, three days before they welcome Chelsea to Wanda Metropolitano for the first leg of their Champions League encounter.
Dembele is yet to make his debut for Atletico since arriving on loan from Lyon on January 13.
He has signed with Diego Simeone's side until the conclusion of the 2020-21 campaign, with an option for the Spanish club to buy for €33.5 million (£30m/$41m) with a potential €5m (£4.5m/$6m) in bonuses. Atletico Madrid will pay a €1.5m loan fee as part of the deal as well.
Dembele spent the last two-and-a-half years with Lyon, having originally signed from Celtic for €22m (£20m/$27m) in the summer of 2018. The French forward scored 45 goals in 108 appearances for the Ligue 1 side during that period, and helped the French club to the Champions League semi-finals in 2019-20.