Lionel Messi was stretchered off with a knee injury as Barcelona drew 0-0 with Benfica at the Camp Nou, a result which saw Celtic go through at the expense of the Portuguese from Champions League Group G.
The club later confirmed the injury was only bruising to the left knee, but added that the Argentine "is still awaiting more tests to determine the extent of the injury".
Benfica needed only to match Celtic's result against Spartak Moscow and they wasted a number of excellent chances against a weakened Barca, especially in the first half and were to rue them as Celtic snatched a 2-1 win over Spartak Moscow.
Messi was brought on as a second-half substitute but went down clutching his knee late on in the game.
The Catalan side cruised through the group stage with just one defeat, away to Celtic, in what has been a prolific start to the season where domestically they have established a new record of 13 wins from 14 games.
Fans turned up hoping to see Messi match or better Gerd Mueller's record of 85 goals in a calendar year but in the end the night finished on a sour note with the Argentine still a goal behind.
"It doesn't appear too serious as it is a knock to his knee but he will have to have tests now to find out exactly what the situation is," said coach Tito Vilanova.
"He is calm although a little worried as you would expect for a player with an injury who is waiting to know how serious it is.
"I played him for the last 30 minutes to give him a run out and he didn't play just to break the record as if that had been the case then he would have started.
"A player can get injured at any moment and at the end of the day we are Barcelona and we are playing in the Champions League."
Barca chose to rest the bulk of the regular side and took the opportunity to blood youngsters in the true spirit of the club which takes such pride in the production line from their Masia academy.
Benfica's task of toppling the Catalan giants was made more difficult by the loss of a number of important players, including Pablo Aimar, Enzo Perez and Eduardo Salvio.