Real Madrid face an anxious wait to discover the extent of Gareth Bale's ankle injury after the holders secured their place in the Champions League knockout stages with a 2-1 win over Sporting Lisbon.
Bale hobbled off just before the hour mark at Estadio Jose Alvalade.
The Welshman, who had been in impressive form for Real, could now be facing a race against time to be fit for El Clasico against Barcelona on December 3 as well as the table-topping showdown with Group F rivals Borussia Dortmund.
Real coach Zinedine Zidane said in his post-match press conference: "Gareth Bale suffered more of an ankle twist than a knock, but we will have to wait and see what the problem is.
"Tomorrow (Wednesday) he will be examined by our medical staff and after that we will find out (more)."
A draw on Tuesday night would have been enough to send Los Blancos through alongside Dortmund, who romped to a Champions League record 8-4 win over Legia Warsaw and will now come to Madrid next month in a showdown for top spot.
It appeared Zidane's side would be left with just that after a penalty from Adrien Silva after 81 minutes had cancelled out Raphael Varane's first-half opener, with the home side having seen defender Joao Pereira sent off after appearing to punch Mateo Kovacic.
However, with just three minutes left, Benzema nodded in a weighted cross from Sergio Ramos to secure victory as Real extended their unbeaten run to 30 games in all competitions.
Zidane, who had made just one change to the side which beat city rivals Atletico 3-0 at the weekend, was pleased with the way the team went about their job in Portugal.
"We had our difficult moments in the game but that is normal," he said.
"In the previous game against us Sporting played with the same intensity and they didn't drop their heads after going behind.
"But we managed to score a wonderful second goal through Karim Benzema.
"It was important that we won here; we achieved what we came to get. We are going to play a final against Dortmund now."
Next up for Real is a home match against Sporting Gijon and then the second leg of their Copa del Rey tie against Segunda Division B side Cultural Leonesa, which they lead 7-1.
Zidane said: "What we want to do is to continue working hard in order to achieve our objectives. We must look to recover because it isn't easy for these players playing every three days."
Sporting, meanwhile, must now focus on getting the required result from their final Group F tie away to Legia Warsaw to secure third spot and progression to the Europa League.
Coach Jorge Jesus said: "The difference between the two sides was only in the final result.
"In the game Sporting was equal to Real Madrid, tonight the red card for Joao Pereira was decisive.
"We were great both technically and tactically. We only missed a few details.
"My players did well and, with time, they will learn not to fail in those small details."