Champions Barcelona and English league winners Chelsea will renew their stormy rivalry after they were drawn in the group stages of the Champions League on Thursday.
It was the third time in three years that Barcelona, who beat Chelsea in the second round of last season's competition, have been paired with the London club.
The two teams will also meet Werder Bremen, who finished second in the German Bundesliga last season, and debutants Levski Sofia of Bulgaria in Group A.
"The third time in three years, it's a big draw," said Chelsea chief executive Peter Kenyon. "But we must not overlook the other teams, there's all to play for now."
"The Holy Grail is lifting the Champions League and players like [Michael] Ballack and [Andrei] Shevchenko will bring their experience," he said. "We have great respect for Barcelona as a team, and good relations with them as a club."
"But we must concentrate on getting through. Winning [group] games is important not only to qualify but to improve co-efficients [the factor used to determine seedings in next year's draw]," Kenyon said.
Last season's losing finalists Arsenal will face 2004 champions Porto and have potentially tricky trips to Hamburg of Germany and CSKA Moscow in Group G.
"I'm quite happy with Hamburg. We finally get to play a German club," said Arsenal's German international goalkeeper Jens Lehmann.
"I think Sporting and CSKA Moscow are good teams but we have the favorites position in this group. As for Hamburg, they're always dangerous in set pieces and you always have to be aware of this," he said.
Hamburg coach Thomas Doll was satisfied with the group.
"It's a great draw for us. Our goal is to reach the quarter-finals. It's possible even if Arsenal and Porto will be favorites," he said.
The group stages of European soccer's most prestigious competition also saw 2005 winners Liverpool drawn with Dutch champions PSV Eindhoven, Bordeaux and Turkey's Galatasaray in Group C.
Liverpool chief executive Rick Parry said he was happy to have avoided a draining trip to Romania, Russia or Ukraine.
"PSV and Bordeaux are a little bit of an unknown for us," said Parry. "Turkey's a long way but we've avoided Eastern Europe. It's okay. We're looking forward to it."
Spanish giants Real Madrid were drawn in the same pool as five-time French champions Lyon, as they were last year.
Completing Group E are Steaua Bucharest of Romania and Ukrainian club Dynamo Kiev.
A "Battle of Britain" scenario was set up in Group F as Manchester United were drawn with Scottish champions Celtic.
Also in the mix were Benfica of Portugal and Danish debutants FC Copenhagen.
"We're looking forward to Celtic, and Benfica put us out last year so there's a chance for revenge," said Manchester United chief executive David Gill.
Inter Milan were drawn with German champions Bayern Munich in Group B alongside Sporting Lisbon and Spartak Moscow.
"We have strengthened our squad this summer and our coach Roberto Mancini has lots of options. We feel we can go all the way in every tournament that we are competing in," Inter director Gabriele Oriali said.
Group D saw Valencia pooled with Roma, Olympiakos of Greece and Ukrainian club Shakhtar Donetsk.
AC Milan, found guilty in the match-fixing scandal in Serie A but reinstated on appeal, had a favorable draw in Group H against Lille, AEK Athens and Belgian outfit Anderlecht.