Lewandowski was set to miss the match after the Spanish football federation (RFEF) banned the Poland international for three games following his sending off in Barcelona's 2-1 win at Osasuna in November.
The 34-year-old was shown a yellow card for dragging back Nacho Vidal in the 11th minute and 20 minutes later received his second after appearing to elbow David Garcia in the face.
According to the RFEF Officiating Committee, Lewandowski was given a three-game ban due to a gesture towards the official after he was shown the red card that was of "contemptuous attitude towards the referees".
Last month, Barcelona said they would appeal the ban. According to reports in Spanish media, their appeal was rejected by the Court of Arbitration for Sport (CAS) earlier this month.
In a statement on Friday, Barcelona said a "dispute settlement court in Madrid issued a precautionary measure against the suspension," clearing Lewandowski to play.
"We found out after training had finished, we were preparing for the game thinking that we could not call on him," Xavi told reporters ahead of Saturday's game against city rivals Espanyol.
"It's not the best timing, but we are happy that he can play. He was also surprised by the timing. For me it's a disproportionate ban.
"Now the committee of referees has between two and three days. It would be good to know how long the sanction is, when we won't be able to count on him. It should have been known before. The organisation is not good."
Xavi added that Ronald Araujo was also back in the squad, but said the Uruguayan defender would not start against Espanyol.
The 23-year-old Araujo sustained a thigh injury during Uruguay's 1-0 defeat by Iran in a friendly in September.
He missed a number of games for Barcelona after undergoing surgery, before travelling to Qatar as part of Uruguay's squad for the World Cup.
"We were with him at the World Cup. We spoke to the coach. In the end, the player's feelings decide," Xavi said. "This week he has been good. He gives everything. We will be cautious. He won't start. Maybe a few minutes, if not in the next match."
Barcelona have a two-point lead over Real Madrid at the top of the table after 14 games.