Roma forward Mohamed Salah has been ruled out of this weekend's Eternal City derby due to ligament damage in his right ankle.
The Giallorossi confirmed the news with a statement on their website that was unable to confirm the length of time for which the Egypt international will be sidelined for.
"Mohamed Salah underwent tests on Thursday that revealed damage to the exterior ligaments on his right ankle, also affecting the front and lateral muscles and tendons," the statement read. "On Friday the player will have further tests to determine the proper treatment plan and expected recovery time."
His absence will come as a blow to coach Luciano Spalletti as his side look to defend their one-point advantage over city rivals Lazio and keep their noses in front with a win or draw at the Stadio Olimpico.
Goalkeeper Wojciech Szczesny is not in two minds about which Rome club are better, however, saying that victory in Sunday's derby would be another step towards their ultimate goal of winning the Scudetto.
"Lazio are having a great season and Roma have missed a few opportunities and there is only one point between us now, but it should be more and if you ask me who are the better team then I have no doubts that it is us," the Poland goalkeeper told Il Corriere dello Sport.
"It's up to us to prove it on the field. I hope there are four points between us on Sunday evening.
"I came back to Roma because I want to win. There are plenty of games to go so anything is still possible, but right now it's best to focus on the derby.
"If we win it, we will be one step closer to our final objective. We need to take things one step at a time and try to get three points in every game. I don't want to get too far ahead because there are still six months of the season to go, but we all have this objective."
Szczesny is not thinking beyond Sunday, let alone beyond June, when his season-long loan from Arsenal expires.
"I don't think that far ahead," he said. "If I start thinking about July 2017, I'm not able to concentrate on what I'm doing now, so I prefer to live in the present."