Following the first round of matches earlier this month, the group stages of this season's Champions League are now off and running.

This week the second batch of encounters will take place and here Sports Mole has selected five things to look out for over the course of Tuesday and Wednesday night.

Mourinho heads home

Chelsea's recent results in the Premier League have heaped pressure on Jose Mourinho, so the 52-year-old may well be relishing a return to the familiar surroundings of the Estadio do Dragao on Tuesday night.

He arrived at Porto in 2002 as a managerial novice, yet by the time that he had departed for West London in 2004, the Dragons had won two Primeira Liga titles, the Taca de Portugal, the UEFA Cup and the Champions League.

Of course, this will not be Mourinho's first meeting with his former employers as boss of the Blues. He took Chelsea back to his old stomping ground during the 2004-05 campaign, yet it was Porto that were celebrating come the final whistle. Damien Duff gave the Premier League side a half-time lead, but the hosts ran out 2-1 winners thanks to second-half goals from Diego and Benni McCarthy.

English trio need wins

The first round of matches in the Champions League has resulted in more question marks over the standard of English football. Chelsea may have beaten Maccabi Tel Aviv, but all three of their compatriots tasted defeat.

With the greatest of respect, it was average opposition at best in the form of PSV Eindhoven and Dinamo Zagreb that got the better of Manchester United and Arsenal respectively. As for Manchester City, they lost 2-1 at home to Juventus, who despite being a big name in European football, lost some key players over the summer and have started the new Serie A season slowly.

With qualification for the knockout stages in mind, all three clubs must now avoid defeat - and preferably win - their second group games. Losing the opening two games does not necessarily spell the end of their chances of reaching the last 16, but it makes it a damn sight harder. For the record, Man United face Wolfsburg, Man City travel to Borussia Monchengladbach and Arsenal will play host to Olympiacos.

Record-hunting Ronaldo

You would imagine that any player that has scored eight goals in as many outings would be receiving widespread praise, but Cristiano Ronaldo is a different animal. There can be no disputing that sort of goal return, but the fact that the Real Madrid talisman has only scored in two games this term has made some ask if his powers are on the wane.

Yet, Wednesday's trip to the Swedbank Stadion in Malmo will provide Ronaldo with the perfect chance to silence the critics. Ever since he made the £80m move to the Bernabeu from Man United in 2009, records have tumbled at a rapid rate.

The 30-year-old could break the best of the lot, though, against the Swedes. He will head into the contest on 321 goals for Real, two short of Raul's club record, meaning that a hat-trick will see him become the 10-time European champions leading goalscorer of all time. Amazingly, it took the great Raul 741 appearances to reach that total, while Ronaldo has featured in just 307 games in the famous white shirt.

Life without Messi

Barcelona head coach Luis Enrique has many fine players at his disposal, but for the next seven to eight weeks, he is going to have to make do without the best of the bunch - Lionel Messi.

The 28-year-old, who has scored 418 goals in 493 appearances for the Catalan outfit, lasted just 10 minutes of Saturday's 2-1 win over Las Palmas before he limped off with a knee injury. A subsequent scan revealed ligament damage, which has left Barca to solider on without their main man.

The news will have been music to the ears of Roger Schmidt as his Bayer Leverkusen side prepare to travel to the Camp Nou on Tuesday night. The last time that the Germans made the same trip - back in 2012 - they were beaten 7-1, with the free-scoring Messi helping himself to five goals.

Unbeaten records

The financial backing of the Qatar Investment Authority has seen Paris Saint-Germain become France's dominant force - something that Laurent Blanc and his squad will be expected to show in Europe's premier competition this time around.

On Wednesday PSG head for the Ukraine and Shakhtar Donetsk, where they will be putting on the line an unbeaten record that stretches back 17 competitive matches, 15 of which have been won. For good measure, Blanc's men also avoided defeat in all five of their pre-season friendlies.

That run filters into the background, though, when you learn that Dinamo Zagreb have not been defeated in any of their last 45 outings, which dates back to November last year. However, they face Bayern Munich on Tuesday at the Allianz Arena - extending that sequence to 46 would be seen as a great achievement.