Xavi says Barcelona must improve after their 2-1 defeat to Celtic left them short of certain qualification to the last 16 of the Champions League.
The Catalan giants suffered a shock defeat at Celtic Park, going two-goals behind before Lionel Messi scored a consolation in stoppage time.
It leaves them needing to win their final two games to be sure of winning the group and gaining the advantage of playing a runner-up in the next round.
And Xavi says they need to play better to make sure of progression.
He said: "We need a big improvement from how we played against Celtic.
"We have to win the next two games.
"Our next game against Spartak Moscow is now very big, we must win that because we have to win the group.
"But it is in our hands and we know what we need to do."
The Spanish international was left to rue a missed opportunity to end the group as a contest in Glasgow.
"We just couldn't break them down," he continued.
"Celtic managed to take two chances and for that we have to congratulate them.
"Once they went ahead they gave us no space and this time we couldn't come back."
But despite the disappointment Xavi said he had enjoyed the atmosphere at Celtic Park.
"It was wonderful - a great example, " he added.
"I think if they can play with the same spirit against Benfica they can get through to the next round."