Lisbon: Barcelona were humbled 3-0 by Benfica on Wednesday to pile the pressure on coach Ronald Koeman with the Spanish club's Champions League hopes hanging by a thread.
Barca are bottom of Group E with no points from two games, six behind leaders Bayern Munich and four adrift of Benfica.
"At the end of the day, they easy thing is getting rid of the coach, but we are all responsible. The truth is we're in a critical situation," Barca captain Sergio Busquets said.
"We're only two games into the group stage. We need to focus on improving.
"We need to win our next two games against Dynamo Kiev and see how the other two get on. There's a long way to go and we need to try and be positive."
Things started badly for the Catalans as Darwin Nunez opened the scoring after three minutes with a neat near-post finish.
Lucas Verissima made a last-ditch block to deny Luuk de Jong from close range as Barca looked to get back into the game, but they were second best throughout.
Their plight was summed up on the half hour when Koeman substituted Gerard Pique, who had been booked and lucky to avoid a second yellow, for 17-year-old midfielder Gavi.
Nunez almost added a second five minutes after the break when he hit the post from distance after beating Marc-Andre ter Stegen to a through ball.
With 21 minutes left Jorge Jesus's side got their reward as Rafa Silva fired in from close range after Ter Stegen had denied Joao Mario.
Nunez doubled his tally from the penalty spot on 79 minutes after VAR spotted a handball by Sergino Dest.
Eric Garcia was sent off for a second yellow card three minutes from time as a bad night turned to worse for Barca, and the defender will miss the must-win home game against Dynamo Kyiv next month.