The 28-year-old has not even travelled to Spain with the rest of the Milan squad to face his former employers.
However, chief executive Adriano Galliani said it was not a big problem for the Italian champions.
"We're calm and relaxed, we'll play Pato and (Antonio) Cassano, who are two great players," he told reporters.
"I don't like feeling sorry for myself. We're champions of Italy and we're not going to play a knock-out match, there will be others so we'll continue calmly."
"Barcelona are the best team in the world but we're the one with the most (international) trophies."
"We'll play as we always have in the best stadiums in the world, it will be a footballing party."
Milan and Barcelona are the overwhelming favourites to progress from Group H which also includes minnows Viktoria Plzen and BATE Borisov.
Ibrahimovic, who scored 14 goals in 29 league games last term, claimed his eighth league title in a row and ninth in total with five different clubs across three countries.
He joined Milan on an initial one-year loan deal after just one year in Spain following a trade worth more than €50 million that sent Cameroon's Samuel Eto'o to Inter Milan.
Despite scoring 21 goals in 41 games in his debut season, the tall Swede spent much of the 2009/2010 season run in on the bench for the Catalans and his year with the club is widely considered to have been underwhelming.