Erik ten Hag takes his side to Estadio do Dragao on the back of a 3-0 reverse at the hands of Tottenham Hotspur.
The Red Devils were thoroughly outclassed by the North Londoners, who condemned them to a third defeat in six Premier League fixtures during 2024-25.
Having also only posted a 1-1 draw with FC Twente in their first match of this competition, Ten Hag is under pressure to deliver a bounce-back win.
Here, Sports Mole rounds up Man United's injury and suspension news ahead of their contest with the Primeira Liga giants.
Leny Yoro
Status: Out
Type of injury: Foot
Possible return date: December 3 (vs. Arsenal)
Yoro will be out until at least the start of December due to the fractured metatarsal that he suffered during a pre-season clash with Arsenal, with his debut for the club potentially coming against the Gunners in the Premier League.
Tyrell Malacia
Status: Out
Type of injury: Knee
Possible return date: Unknown
Malacia missed the entire 2023-24 season due to a serious knee injury which required two separate operations, and the left-back is still not ready to return, but he was able to take part in the warm-up part of the club's training session last week.
Luke Shaw
Status: Out
Type of injury: Calf
Possible return date: October 6 (vs. Aston Villa)
Shaw has been absent early in the season due to a calf problem, but the left-back is closing in on a return to action, potentially before the October international break.
Mason Mount
Status: Major doubt
Type of injury: Head
Possible return date: October 6 (vs. Aston Villa)
Towards the back end of Sunday's match, Mount suffered a nasty head injury in an aerial duel with Radu Dragusin. With blood pouring from the back of his head, the midfielder was withdrawn, and he is now a major doubt for the trip to Portugal.
Harry Maguire
Status: Major doubt
Type of injury: Knock
Possible return date: October 3 (vs. Porto)
Maguire had been expected to be named in the squad against Spurs, only for the centre-back to be a notable absentee. It has since been reported that the England international picked up a knock in training, albeit it yet to be determined whether he will be available for this contest.
Kobbie Mainoo
Status: Major doubt
Type of injury: Muscle
Possible return date: October 3 (vs. Porto)
Mainoo needed to be withdraw before half time against Spurs with an unspecified issue. However, given that the England international hobbled off ahead of the break, Ten Hag has acknowledged that the youngster may struggle to be fit in time for Thursday.
MANCHESTER UNITED'S SUSPENSION LIST
Man United have no players suspended for this encounter.