After numerous qualifying rounds, the group stages of this season's Champions League will get underway tomorrow evening.

Here, Sports Mole has selected five of the biggest talking points ahead of the opening round of fixtures.

The return of Memphis

It would probably be fair to assume that when Memphis Depay swapped PSV Eindhoven for Manchester United in a deal worth £25m this summer, he did not expect to be running out at the Philips Stadion again any time soon. But, as it has transpired, PSV vs. United is first on the agenda this Tuesday.

Depay is bound to have fond memories of his stint with the Boeren, having helped them to win the Eredivisie title last term for the first time in seven years by scoring 22 goals. That contribution made him a popular figure in Eindhoven, yet former PSV head coach Aad de Mos has claimed that Depay could be in for a rough ride. New teammate Ashley Young has backed the 21-year-old to cope with the pressure, while current PSV boss Phillip Cocu spoke glowingly about the youngster during a recent interview with the Sunday Times.

Talking of Cocu, this encounter will see him reunited with United manager Louis van Gaal, having previously worked under his fellow countryman's guidance at Barcelona and the Netherlands national side.

Enrique back in Rome

"I'm leaving because I feel very tired and drained. I've given everything this season. I don't think I'll be able to recover my energy over the summer - not the energy needed to motivate a group. I definitely won't be coaching next season, though I don't know if I'd even have had any offers."

Those were Luis Enrique's words upon his decision to resign as Roma head coach in 2012 after just one campaign at the Stadio Olimpico. Having impressed during a spell in charge of Barcelona B, Roma gambled on the Spaniard. It was to be a botched experiment, though, as La Maggica missed out on a place in Europe, thanks largely to their 14 Serie A defeats.

It was a stint that some predicted had ended the 45-year-old's chance of becoming a world-class manager, but having resuscitated his career at Celta Vigo, Enrique guided Barcelona to the treble last term. On Wednesday he will head back to the Italian capital, three years after his departure.

Debutants head for Lisbon

Not only will FC Astana be making their Champions League debut, they are also the first ever club from Kazakhstan to have reached the group stage. The Blue and Yellows had to come through an arduous qualifying campaign, which included two-legged wins over NK Maribor, HJK Helsinki and Cypriot outfit APOEL.

In head coach Stanimir Stoilov they have someone that played for a host of clubs during his career - including Fenerbahce - while the 48-year-old has had two separate stints in charge of his native Bulgaria. As for the playing squad, that is made up largely of Kazakhstan internationals.

They will make their bow in Lisbon at the home of Benfica on Tuesday night. The Portuguese champions have won this competition twice before, although they have not triumphed since the 1960s.

Ibrahimovic reunion

Zlatan Ibrahimovic may not come across as an emotional figure, but even the big Swede may have a tear in his eye when his Paris Saint-Germain side walk out against Malmo at the Parc des Princes on Tuesday night. After all, the 33-year-old was born in the Swedish city and started his career with Di Blae - a time that he reflects on with great affection in his autobiography.

In true Ibrahimovic fashion, he got tongues wagging recently regarding a potential playing return to Malmo when after they had overcome Celtic to reach the group stages (before the draw was made) he tweeted: "One day I hope to experience the Champions League in Malmo on the pitch. Congratulations!"

His PSG teammate Blaise Matuidi recently told Telefoot: "Ibra is very happy to play against the club where he started. This may be his last Champions League, so playing against his hometown team is something beautiful."

Farewell Mourinho?

We've been here before with Jose Mourinho and Chelsea. All was not well at Stamford Bridge at the start of the 2007-08 campaign and following a 1-1 home draw with Rosenborg in the Champions League on matchday one, the self-proclaimed 'Special One' was sent packing by Roman Abramovich.

Back then, the West Londoners had lost just one of their opening six Premier League games, whereas this time around three defeats have already been suffered in one less outing. Mourinho has insisted that he is calm, but his alleged f-worded rant aimed towards his Everton counterpart Roberto Martinez at the weekend would suggest that he is indeed getting a little hot under the collar.

The Portuguese boss has also stressed that his job is safe, which is probably right. Yet, the knives will be sharpened were Maccabi Tel Aviv to pick up an unexpected positive result, just like Rosenborg did - to Mourinho's cost - eight years ago.