Luis Enrique faces a return to the Stadio Olimpico as Barcelona begins its Champions League defense against Roma on Wednesday.

The former Spain international was in charge of Roma for the 2011-12 season but left after failing to guide the club into European competition.

But Luis Enrique, who guided Barca to the treble last term, says his experience in the Italian capital was a key learning curve in his coaching career.

"What happened at Roma made me a better coach," he said. "I have great memories, I'd have liked to have finished higher but it was a very positive year."

The game also represents another milestone in the career of Lionel Messi, with the Champions League's all-time top scorer set to make his 100th appearance in the competition.

The Argentina star came off the bench to score the winner against Atletico Madrid at the weekend, having been left out of the starting lineup after missing training to be at the birth of his second child, but is expected to start in midweek.

Thomas Vermaelen and Claudio Bravo (both calf) are sidelined, while Dani Alves has not recovered sufficiently from a groin injury, but Gerard Pique is free to return after missing recent domestic action due to suspension.

Roma sealed a 2-0 win over Frosinone at the weekend and debutant Antonio Rudiger hopes to see the team carry confidence into the showdown with Barca.

"I think we played well," he told the club's official website. "It wasn't a stellar performance like the Juve match [a 2-1 win before the international break] but the most important thing was to get the three points. Now we can focus on Barcelona."

Roma will be without Miralem Pjanic (calf) for the game but Radja Nainggolan is set to start after only appearing as a substitute against Frosinone.

The European champions overcame Roma 3-0 in the Joan Gamper Trophy exhibition match in August but they have not met in the Champions League since February 2002, when Luis Enrique started in Barca's midfield in a 1-1 draw.

Francesco Totti, who also played in that fixture, is one goal short of 300 for Roma in all competitions.