Poland international Lewandowski was shown two yellow cards in the first half of Barca's last match before the World Cup break – a 2-1 win at Osasuna in November.
The Spanish Football Federation (RFEF) issued Lewandowski with an extended three-game punishment due to an alleged gesture made towards referee Gil Manzano after being dismissed, although the player said it had been aimed at his own coach, Xavi.
Lewandowski has claimed the suspension is "too much for what I did" and the former Bayern Munich man said it would be "painful" to sit out three games.
With 18 goals in 19 games this season, to lose Lewandowski for three games would deny Barcelona the services of its deadliest attacking weapon.
Only Erling Haaland (26) and Kylian Mbappe (20) have scored more club goals this season, among players in Europe's top five leagues.
The full ban may yet apply but for now it is on hold, a surprise development, particularly in regard to the timing.
Barcelona said in a statement on Friday: "Lewandowski can play tomorrow against Espanyol after the dispute settlement court in Madrid issued a precautionary measure against the suspension imposed by the court of arbitration for sport."
The Espanyol game is Barcelona's first since the World Cup break, with Xavi's team having sat top of LaLiga heading into the six-week interval.
It has dropped to second, a point behind champion Real Madrid which accounted for Real Valladolid 2-0 on Saturday (AEDT).
"We have been facing this week different options, taking into account that Robert was not available, but in the end it's fantastic news we will be able to have Robert, although it's not the best situation to know a day before that he's going to be able to play," Xavi said.
"He's surprised about timings but I've said it plenty of times: it was an unfair suspension, three games for just touching the nose."
On the flip side, Espanyol is furious.
Los Pericos suggested the decision threatens the integrity of the competition because the round of matches has already started, while it is bewildered why such a ruling has been given when Lewandowski's sanction had been supported by three bodies: LaLiga, the appeals committee and CAS.
Espanyol's statement read: "Espanyol finds it unusual that, 24 hours before the match against Barcelona, and after it was rejected by different competent bodies (competition, appeal and CAS), a precautionary measure has been granted to a previously imposed sanction to the Barcelona player, Robert Lewandowski.
"In this sense, as an indirectly involved party, we were only able to have access to the resolution after requesting it from different bodies and not because it was communicated to us, as established by the procedural regulations.
"However, we believe that the requirements are not met to justify the precautionary measure. Specifically, the appearance of good law is particularly indefensible as there are two sanctions of different types, three unfavourable administrative resolutions and an arbitration act with a presumption of veracity that support the sanction.
"Likewise, there is talk of irreparable damage to Barcelona without assessing the irreparable damage to its rivals and the competition without giving the possibility of any recourse.
"The club considers that this last-minute decision completely conditions this matchday, which started yesterday (Thursday), and the team's preparation for this match. RCD Espanyol understands that it is a grievance and an injustice considering the precedents with other clubs.
"Despite this injustice and this unprecedented decision in the competition, our team tomorrow will compete 110 per cent to live up to the trust of our fans."