The Red Devils have been working around a plethora of absences all season long, as Luke Shaw, Leny Yoro, Kobbie Mainoo, Tyrell Malacia and Harry Maguire are currently in the treatment room.
Man United were also handed a fresh concern over Lisandro Martinez earlier in the international break, potentially depriving Amorim of a key defensive option before his maiden match at the helm.
Now, the former Sporting Lisbon head coach could be missing former teammate Lindelof, whom he briefly played alongside at Benfica, as the 30-year-old hobbled off in the 26th minute of his side's 2-1 win over Slovakia.
At this early stage, it is still unclear how severe Lindelof's problem is, but the centre-back is highly unlikely to be involved in Tuesday's Nations League finale against Azerbaijan.
Lindelof blow adds to Man United defensive woes
The 30-year-old has been bedevilled by a series of fitness problems since making the switch to Man United in 2017, missing a total of 48 matches for club and country due to injury or illness.
Lindelof spent several weeks on the sidelines last term with groin and hamstring problems, and a toe injury also delayed his start to the 2024-25 campaign, in which he has made just seven appearances so far.
The former Benfica man has only made the first XI in the Europa League and EFL Cup this season too, making just four substitute appearances in the Premier League totalling 58 minutes.
Lindelof will soon enter the final six months of his deal at Old Trafford, and a move away at the end of the season is expected to materialise due to his status as a bit-part player.
AC Milan advisor Zlatan Ibrahimovic has talked up the prospect of Lindelof playing at San Siro, but the Man United man recently affirmed that he is only focused on his immediate future at Man United.
When could Man United's other injury victims be back?
Lindelof is now one of six troops in the Man United infirmary, although there is a good chance that the medical bay will start to clear out as Christmas draws nearer.
Luckless left-back Malacia played 45 minutes for the Under-21s in an EFL Trophy loss to Huddersfield Town in midweek, so a senior comeback should not be too far away for the Dutchman after his serious knee issue.
Maguire (calf) and Mainoo (thigh) are also thought to have good chances of coming back straight after the international break, as might back victim Martinez, but Yoro (foot) and Shaw (calf) may not return until December.
Amorim's first game in charge of Man United comes away to Ipswich Town on November 24, four days before his Old Trafford debut against Bodo/Glimt in the Europa League.