Lionel Messi was carried off on a stretcher late in Barcelona's scoreless draw with Benfica, while Celtic secured a place in the Champions League group stage by securing a 2-1 victory over Spartak Moscow.
A source close to Messi told ESPN Deportes that the injury to his knee is not serious, and he underwent an MRI to know the extent of the damage.
"Messi has a bruise on the outside of his left knee," Barcelona said on its Twitter feed. Later, the club issued a statement that tests revealed no further damage, and it is possible that Messi could recover in time for Barcelona's next game.
For Barcelona, much of the prematch build-up had focused on Messi, with the prolific Argentina forward just one goal away from matching Gerd Muller's 1972 mark of 85 goals in a calendar year.
But the three-time Ballon d'Or winner was named on the bench in Tito Vilanova's much-changed lineup that included eight B team players, with Javier Mascherano, Jordi Alba, Xavi, Andres Iniesta and Cesc Fabregas among the star names not included in the matchday squad.
Messi came on as a sub in the second half and had played about 25 minutes when he burst through down the right but was pushed wide by Benfica goalkeeper Artur, who then got back to his line just in time to save Messi's effort.
Messi's left knee collided with the right hand of Artur. Messi then immediately pulled up, clutching the back of his leg and was carried off on a stretcher, leaving Barcelona, which had already made three changes, to finish the game with 10 men.
"Had we been worried just about the record we would have played Messi right from the beginning," Barcelona coach Tito Vilanova said. "But we had talked about it and decided to bring him on with half an hour to play."
Benfica struggled to get any sights of goal in the closing stages and, when they did come, they were passed up by substitute Oscar Cardozo and then Maxi Pereira in the 96th minute.
In Scotland, Kris Commons' dramatic late penalty gave Celtic victory over Spartak Moscow.
Striker Gary Hooper opened the scoring in the 21st minute when he capitalized on a mistake by Spartak defender Juan Insaurralde, but that lead was canceled out in the 39th minute by Ari, after good work by the impressive Emmanuel Emenike.
But the Scottish champions were not to be denied and, after defender Marek Suchy conceded a penalty in the 80th minute for a clumsy barge on Georgios Samaras, up stepped Commons to slam the ball in off the bar.
Two minutes from time, Spartak midfielder Kim Kallstrom picked a second yellow card for a foul on Commons, who was taken off on a stretcher. It was the only sour note in a momentous night for Neil Lennon's side, who finished second in Group G behind Barcelona with 10 points and are in the knockout stages for the first time since the 2007-08 season.
"People laughed at me when I said at the start that my target was to qualify," Lennon said. "No one gave us a prayer going into this group but we have qualified and deservedly so. I think you could see the players progressing last year. We have some really talented players who I felt could play at European level.
"I didn't want them just to be remembered for beating Barcelona but we have beaten Barcelona and qualified for the last 16 and that is a fantastic feather to have in your cap."
Benfica was condemned to third place in Group G and a place in the Europa League.
Information from Press Association and The Associated Press was used in this report.