Jose Mourinho may be thankful to return to happy surroundings on Tuesday when he takes his ailing Chelsea side to former club FC Porto on Matchday Two of the Champions League. It was at Porto that Mourinho achieved perhaps the greatest feat of his career, when leading the Portuguese side to the Champions League title in 2005. Since then, his coaching career has largely continued on an upward trajectory, adding league titles in England, Italy and Spain as well as a second European Cup with Inter Milan. Yet he now returns there in the midst of perhaps the most difficult period of his career.

After Chelsea began their Champions League campaign with a 4-0 win over Maccabi Tel Aviv, and followed it up by beating Arsenal in the Premier League and Walsall in the Capital One Cup, it appeared they were righting their turbulent early season ship. On Saturday, however, the form that had seen last season’s Premier League champions lose three of their first five games was back on display.

At St James’ Park, Chelsea trailed 2-0 to a Newcastle United side that had yet to win in the Premier League all season, with Mourinho admitting their first-half performance had been as bad as any he’d overseen during his two spells in charge of the club. Not for the first time this season, the Portuguese claimed he wished he was able to make more than just the three substitutions, such was the standard of some of the individual performances.

It was only in the closing minutes of the contest that Chelsea began to show any signs of the team of last season, although that proved enough to salvage a point thanks to goals from substitutes Ramires and Willian. While their victory against the Israeli champions two weeks ago means that Chelsea have some breathing room in the Champions League ahead of the trip to Portugal, all at the club will be keen for a much improved performance.

Unlikely to feel any sympathy for Mourinho’s current struggles is the man who will start in goal for Chelsea’s opponents at the Estádio do Dragão. Iker Casillas’ 25-year association with Real Madrid came to an end in the summer when he departed for Porto. But it was during Mourinho’s time in charge at the Bernabeu that his fall from icon status began.

Casillas was dropped midway through Mourinho’s final season at Real Madrid, in a decision reportedly based on a personal falling out as much as the Spaniard’s ability between the posts. The World Cup winner continued to divide opinion among coaches and supporters until moving on for a new challenge in Portugal.

The start to his Porto career has so far gone well, with his new club going unbeaten through seven games at the start of the season. As well as sitting top of the Portuguese Liga table, Porto began their Champions League campaign with a 2-2 draw at Dynamo Kiev.

Quarterfinalists in the competition last year, Porto are likely to welcome back big summer signing Giannelli Imbula and striker Vincent Aboubakar from the team that came away with a point from Moreirense on Friday. Chelsea will again be missing goalkeeper Thibaut Courtois, but Diego Costa is able to play while he continues to serve his domestic suspension.

Prediction: The lack of intensity visible in several Chelsea players remains startling, and it took until being 2-0 down on Saturday for the team to show any real purpose. A similar performance on Tuesday and Porto have more than enough quality to ensure that the Premier League champions leave empty handed. Still, the return of Diego Costa could help Chelsea to secure a welcome point.

Predicted score: Porto 1-1 Chelsea