The Poland international was also at fault for one of the goals in the first game at Old Trafford where Celtic lost 3-0.
But Bhoys midfielder Barry Robson backed his keeper and did not hold him responsible.
The Scotland international said: "We hung in there in the second half but lost a disappointing goal.
"From where I was standing, I could see the ball was all over the place so it was hard for Artur.
"And you know how well Ronaldo can hit these balls. But overall, we did okay. It was a hard game but we got a decent result.
"I think we can still qualify for the knockout stages.
"If we win our next two games then we are right in there with a great chance."