Barcelona and Juventus will face a Champions League rematch at the group stage after being drawn together in Group D on Thursday.
The two clubs met in last season's quarter-finals, with Juve triumphing 3-0 on aggregate after a convincing first-leg win in Turin.
Massimiliano Allegri's side went on to advance to the final only to be beaten by Real Madrid.
Olympiacos and Sporting complete the group and will face an uphill struggle to deny two of Europe's big guns a place in the knockout stage.
Sporting finished bottom of their group last season, while Olympiacos were eliminated by Hapoel Be'er Sheva in the third qualifying round.
Matches will kick off on September 12, with the group concluding on December 5.
GROUP D TABLE
GROUP D FIXTURES
|Sep 12||Barcelona vs Juventus||19:45|
|Sep 12||Olympiacos vs Sporting||19:45|
|Sep 27||Sporting vs Barcelona||19:45|
|Sep 27||Juventus vs Olympiacos||19:45|
|Oct 18||Juventus vs Sporting||19:45|
|Oct 18||Barcelona vs Olympiacos||19:45|
|Oct 31||Sporting vs Juventus||19:45|
|Oct 31||Olympiacos vs Barcelona||19:45|
|Nov 22||Juventus vs Barcelona||19:45|
|Nov 22||Sporting vs Olympiacos||19:45|
|Dec 5||Barcelona vs Sporting||19:45|
|Dec 5||Olympiacos vs Juventus||19:45|