Striker Miroslav Klose is "highly unlikely" to play in the second leg of Lazio's Champions League playoff tie against Bayer Levurkusen, his manager Stefano Pioli said.
Klose came off at half-time on Wednesday after injuring his hamstring during Lazio's 1-0 win, but the Italian side face the prospect of travelling to Germany without their star forward.
Stefan de Vrij also left the game on a stretcher late on after a clash of heads, but Pioli said Klose's injury was the more severe.
"De Vrij seemed all right and I was almost angry," Pioli said. "Klose had a muscular problem and I think it is highly unlikely we'll be able to have him in the second leg.
"It's a real problem, as we can't add anyone else to the Champions League list.
"We need to work hard as a team and must improve further if we want a positive result in the second leg."
Klose had a chance to score before the break but his shot hit the woodwork, and the forward admitted he was concerned about recovering in time for next week's second leg.
"When I hit the post my leg was a little extended, and at the next sprint I felt pain at the back of my thigh. We'll see what happens with the tests," Klose said.
"I don't know if I can make it for the second leg. I hope it is not serious."
Keita Balde Diao came on for Klose and scored the winner in the 77th minute.
"We always say that we have a lot more than 11 players, so the substitutes can make the difference and I am very happy for Keita, as he really worked well this summer and this was the result," Klose said.
The German international warned that Lazio still face a tough battle in his country despite leaving their home leg with a slim advantage.
"The result can be good, but it's not over," Klose said. "I have seen many Bayer Leverkusen home games, but I think we can do it, as any draw there will be in our favour.
"This was the first game that really counted this season and we did much better."
Bayer Leverkusen defeated Atletico Madrid, Benfica and Zenit St Petersburg at home in the Champions League last season, and their manager Roger Schmidt remained confident.
"Each team had periods of the game in which they were dominant," Schmidt said. "We still have a chance of qualifying in the second leg, as it's only 1-0 and above all we are playing at home.
"Let us not forget we are enormously strong on home turf. Nothing has been decided yet."