Chelsea manager Thomas Tuchel has revealed that Christian Pulisic has tested positive for Covid-19, with the United States international set to sit out the Blues' derby date with Arsenal as a result.
The Champions League title holders are due at Emirates Stadium on Sunday for a Premier League meeting with their London neighbours.
Pulisic, who opened his goal account for the season in a 3-0 win over Crystal Palace last time out, will play no part against Mikel Arteta's side as he must serve a period of self-isolation.
What has been said?
Chelsea boss Tuchel told reporters when asked for an update on his plans, with Hakim Ziyech and N'Golo Kante in contention to figure: "Christian has unfortunately had a positive test and needs to follow the protocols.
"He's not been training and is not available for the game.
"Hakim and N'Golo both trained yesterday (Thursday) so we need to have a more physically intense session tomorrow (Saturday) and decide tomorrow. Right now, it seems very positive that both can be in the squad for Sunday."
USMNT monitoring World Cup qualifier status
The United States have a World Cup qualifying match against El Salvador on September 2, with Pulisic now uncertain to participate.
Will Lukaku make his debut against Arsenal?
Getty/Goal
While Pulisic's absence delivers an untimely blow to Chelsea's pre-match plans, they do have a new £98 million ($133m) attacker ready to step in.
Romelu Lukaku has been brought back to Stamford Bridge for a second spell, with Tuchel expecting the Belgium international to make his bow as the Blues' new No.9 this weekend.
He said of a big-money addition: "We have one more training session to go but the week was a heavy load.
"He was with the group with the late starters, so it was an overload week so far. Today was low intensity and tomorrow we will have an important session before the match. We hope he will be on the pitch on Sunday and it looks likely."
Is Chalobah in line for new contract?
While discussing team selection matters, Tuchel was also quizzed on his future plans for 22-year-old defender Trevor Chalobah.
The promising youngster scored on his Premier League debut against Palace and is now being lined up for a new contract in west London.
Asked about those discussions, Tuchel said: "He did a fantastic pre-season with us. He is a top player and a top character.
"He took his chance very impressively. He played very good matches in pre-season, performed for 120 minutes against Villarreal and another strong 90 minutes against Crystal Palace.
"It's logical that he stays here. He is a guy we want to keep and this is his status."