"We've not been in our best moment since the international break," said Xavi on Sunday. "Three weeks ago we were flying, and now we're not, we have to improve."
Lewandowski's goals -- nine in La Liga, making him the division's top scorer - have helped Barcelona move top of the table for the first time since June 2020.
The Catalans are unbeaten in the Spanish top flight, but it's a different story in Europe. Successive defeats on the road to Bayern Munich and Inter leave them in desperate need of a win on Wednesday.
Perhaps the worrying thing is Lewandowski has not been missing chances in the past three matches, which might have been a temporary problem, his team-mates have not been creating them.
The Polish forward's accurate finish earned Barcelona a 1-0 win over Mallorca on 1 October, but it was a chance he created himself. He has barely had a sniff of goal in the subsequent two games.
"He was uncomfortable in the second half (against Celta) but so was the whole team," said Xavi. "We have to find him more."
Barcelona's wingers had a poor night at Camp Nou, with Ferran Torres and Raphinha missing chances early on and finding themselves unable to connect with Lewandowski. When Ansu Fati and Ousmane Dembele came on in the second half, the story did not change.
"Maybe they are getting anxious, looking to score," added the coach. "The forwards need goals to generate confidence."
Inter lined up with five defenders at the San Siro and could operate even more defensively on the road, knowing a draw leaves them in a good position.
In Italy, they managed to disrupt Pedri and Gavi, with the creative midfield duo struggling for influence, while the wingers resorted to slinging crosses into the area, which were easily dealt with.
The match, and Barcelona's future in the competition, may come down to whether Xavi can create a supply line for Lewandowski against suffocating defences, determined to stop him.