The Reds escaped their Champions League qualifier first-leg with a 0-0 draw and Reina told liverpoolfc.tv: "We played really bad and it's clear we have to improve for the game at Anfield.
"The positive thing is we got a result, we kept a clean sheet and it's still in our hands. But we didn't play well.
"I don't know if the ball was over the line before I cleared it - I'll have to watch it on TV. Penalty saves are always difficult but, like I say, at least we got the result on the night. But we have to improve."