Barcelona's hopes of making the Champions League knockout stage hang in the balance after they were held at the Nou Camp by Benfica.
On a frustrating night for Xavi's side, 18-year-old Yusuf Demir, on loan from Rapid Vienna, hit the crossbar.
Ronald Araujo had a goal disallowed for second-placed Barca, who stay two points ahead of Benfica in third.
Barca's final group game is away to runaway leaders Bayern Munich while Benfica host Dynamo Kyiv.
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Both matches are on 8 December and it promises to be a tense finale for five-time European champions Barca.
While they are now undefeated in their past three group games, Barca have managed just two goals in five Champions League matches this season.
They will drop down to the Europa League if Benfica win their final match and Barca do not win in Germany.
Benfica defended stoically, closing down attacks with a solid five-man defensive line, leaving Barcelona in control of the ball much of the time.
However, the hosts managed just three attempts on target.
Benfica had a great chance to win it at the end through Haris Seferovic but he could not finish.
Demir is the fifth teenager to start for Barcelona in the Champions League this season - following Pedri, Ansu Fati, Gavi and Nico Gonzalez.
Barcelona boss Xavi: "Benfica came for a nil-nil. They knew how to play for it. That's a big reason why we didn't score.
"The vital thing is that we generated chances. It's a matter of time before the chances go in.
"We missed an opportunity there but we just have to keep going - there's another opportunity coming up in Munich and we just have to take it."
Benfica boss Jorge Jesus: "We left here with a result that still leaves us dreaming. I keep saying the same thing: Barcelona are one of the best teams in the world and we are competing for qualification with them.
"This should make the fans, players and coach proud - today we were at the level of a great team."
BDST: 1523 HRS, NOV 24, 2021