Brendan Rodgers believes his Celtic side were not on song against Valencia, after the Bhoys left themselves with a mountain to climb by losing the first leg of their last 32 Europa League tie 2-0 at home.
Celtic had a penalty shout turned down just minutes into the game, with winger James Forrest going down in the box after a tussle with Toni Lato.
However, despite enjoying more possession, Celtic struggled to land a blow on Valencia and eventually conceded in the 42nd minute, with Denis Cheryshev getting on the scoresheet, finishing from close range after Ruben Sobrino surged into the penalty box and found him.
Celtic were looking to hit back in the second half, but were reeling just four minutes after the restart when Sobrino netted, this time Cheryshev turning provider with a well-placed cross.
The Bhoys brought on Odsonne Edouard and Timothy Weah, and Edouard then saw a penalty appeal turned down.
Celtic continued to huff and puff, but could find no way through a solid Valencia defensive unit.
It finished 2-0 to Valencia and Celtic boss Rodgers admits that his side made mistakes and let the game get away from them.
Rodgers said on BT Sport: "It was a disappointing game to lose considering we made a good start. We were bright, had a good intensity in our pressing and we circulated the ball well.
"At this level you have to concentrate and you can’t put pressure on ourselves. Tonight we put pressure on ourselves.
"But we made too many mistakes, we weren’t creating that passing and it got away from us.
"When you present those chances to a team with that quality they can punish you.
"It’s a disappointing performance in the end", the Celtic manager stressed.
"When you make the number of mistakes we made with simple passes you become a wee bit safe. And that was the story of our game, really."
Rodgers believes it is now essential for Celtic to score the first goal in the return leg in Spain.
"It’s a big challenge for us but if we get that first goal it maybe gives us hope in the tie."
