The Red Devils were convincingly beaten 3-0 on home soil by Tottenham Hotspur on Sunday, while Porto - in stark contrast - cruised to a 4-0 victory over Arouca in the Primeira Liga.
Match preview
Man United have made their joint-worst start to a Premier League campaign, picking up just seven points and losing three of their opening six games, including a miserable three-goal defeat at the hands of Spurs last weekend - one described by former defender Gary Neville as "disgusting" and "one of the worst performances" by a Red Devils team under Erik ten Hag.
The somewhat controversial dismissal of Bruno Fernandes did not help Man United's cause, but their worst spell arguably came when they had 11 players on the pitch, as Tottenham cut through their midfield like a knife through butter, with a whole host of familiar bad habits resurfacing once again.
Ten Hag, who has now suffered 10 defeats as Man United boss by a margin of at least three goals - including two this season already - is running out of excuses to explain the Red Devils' demise. Over £600m has been forked out on new signings and 12 of the 16 players used against Spurs were either recruited by the Dutchman or brought into the first team by him from the club's academy.
If reports are to be believed, Man United's hierarchy have no immediate plans for a change of manager, with Ten Hag set to remain in situ for away encounters with Porto and Aston Villa before the international break. However, if performance levels do not improve quickly, then the under-pressure 54-year-old - who only penned a new two-year contract in July - could be in trouble.
Prior to the defeat against Spurs, Man United laboured to a 1-1 home draw with FC Twente in their opening Europa League fixture, but they can travel to Porto on Thursday with some confidence as they are unbeaten in their last 12 European matches against Portuguese clubs.
The Red Devils beat Porto 1-0 in their most recent meeting at the Estadio do Dragao back in 2009 when Cristiano Ronaldo scored an iconic 40-yard goal to secure a slender Champions League victory. Another win on Thursday should grant Ten Hag more time and would get United up and running in the Europa League before they face Jose Mourinho's Fenerbahce on matchday three.
While Man United are down in the dumps, Porto have made a significantly better start to their domestic campaign, winning six of their opening seven Primeira Liga matches by an aggregate score of 16-1, with their only league defeat during this run coming at leaders and defending champions Sporting Lisbon (2-0) at the end of August.
Porto's most recent success took place on Sunday at home against 10-man Arouca, with second-half goals from Samu Omorodion, Nico Gonzalez, Galeno and Deniz Gul securing a comfortable 4-0 victory and consolidating second place in the table.
Head coach Vitor Bruno, who replaced Sergio Conceicao in the summer, was full of praise for his side's second-half display and hopes they can transfer their domestic form onto the European stage having yet to hit the ground running.
Indeed, Porto suffered a surprise 3-2 away defeat against Norwegian outfit Bodo/Glimt in their opening Europa League fixture last week, despite playing the majority of the second half with an extra man; the Dragons have in fact won only one of their last seven games in Europe's secondary club competition.
Porto have faced Thursday's opponents Man United a total of eight times in Europe and have come out on top only twice - a thumping 4-0 home win back in 1977 in the European Cup Winners' Cup and a 2-1 success in 2004 in the Champions League quarter-finals en route to winning the tournament.
Porto Europa League form:
L
Porto form (all competitions):
W
L
W
W
L
W
Manchester United Europa League form:
D
Manchester United form (all competitions):
L
W
W
D
D
L
Team News
Porto will be without long-term absentees Zaidu Sanusi and Ivan Marcano (both ACL) due to injury, while Otavio has missed the last three games with a muscle issue and remains doubtful.
However, the Dragons were boosted by the return to fitness of Arsenal loanee Fabio Vieira last weekend, with the midfielder coming on as a substitute for the final 20 minutes, and he could be fit to make his first start for the club on Thursday since re-joining in the summer.
Omorodion, who was strongly linked with Chelsea in the summer before joining Porto, scored on his Europa League debut last time out and is expected to lead the line once again, and he could be supported in attack by wingers Pepe and Galeno.
As for Man United, Leny Yoro (foot) and Luke Shaw (calf) remain sidelined, while Kobbie Mainoo (muscle), Mason Mount (head), Harry Maguire (knock) and Tyrell Malacia (knee) are all doubtful. Mainoo was forced off with his issue towards the end of the first half against Spurs.
Either ex-Porto man Casemiro or Christian Eriksen could deputise in midfield alongside Ugarte if Mainoo is not deemed fit to feature, while captain Fernandes is available to continue in the number 10 role despite his Premier League dismissal on Sunday.
With United having lacked a cutting edge in the final third, Joshua Zirkzee now finds his place under threat from Rasmus Hojlund, while Amad Diallo and Antony will continue to battle with Alejandro Garnacho and Marcus Rashford for starts on the flanks.
Porto possible starting lineup:
Costa; Mario, Pedro, Perez, Moura; Gonzalez, Varela; Pepe, Sousa, Galeno; Omorodion
Manchester United possible starting lineup:
Onana; Mazraoui, De Ligt, Martinez, Dalot; Eriksen, Ugarte; Diallo, Fernandes, Rashford; Hojlund
We say: Porto 2-2 Manchester United
Ten Hag is in desperate need of a reaction from his Man United players on Thursday, but success against a Porto outfit who have lost just one of their last 22 home matches (W18 D3) in all competitions is not guaranteed.
The Red Devils' last four European away games have seen a total of 23 goals scored (nine for and 14 against) and they have only won once during this run. Another tricky trip on the road could be on the cards for Ten Hag and co, and they may have to settle for a share of the spoils on this occasion.