Dorgu is returning to Manchester after suffering an injury while representing Denmark, with the club set to carry out further medical examinations at Carrington.
Fernandes, meanwhile, has remained with Portugal despite carrying a fitness concern and could still feature during the international break.
Dorgu was forced off after just 30 minutes of Denmark's 2-0 Nations League victory over Wales on Sunday. The 21-year-old defender received treatment before being substituted, with the injury understood to involve his thigh or hamstring.
Denmark subsequently confirmed that Dorgu would withdraw from the squad. Head coach Brian Riemer also indicated that the defender would return to Manchester and would not be available for the remainder of the international fixtures.
United will now assess the extent of the injury at Carrington. The timing is a concern for the club, with Tottenham due to visit Old Trafford on October 10.
Dorgu has made six appearances for United this season, including three starts, and has contributed two assists. His injury adds to a difficult period for Denmark, who have already lost several players, including Andreas Christensen, Alexander Bah, Albert Gronbaek and Kasper Dolberg.
Fernandes' situation is less definitive. The United captain missed Portugal's Nations League victory over Norway on Sunday after being left out as a precaution.
Portugal manager Jorge Jesus has indicated that Fernandes remains part of the squad and could return for the meeting with Denmark on Thursday.
The midfielder has reportedly been managing an injury since United's Champions League victory over Sabah FK on September 10. Despite the issue, he passed late fitness tests before United's Premier League matches against Manchester City and Fulham and went on to play 90 minutes in both games.
He also featured for the final 20 minutes of United's Carabao Cup defeat to Brighton.
Fernandes has been an important contributor for United this season, scoring four goals and registering one assist. His goals include a Premier League hat-trick against Ipswich Town.
Away from the injury news, United have also completed the signing of 16-year-old Isaac Konde from rivals Liverpool. The teenager played under-18 football for Liverpool last season before making the move to Old Trafford.
Anthony Gordon believes his move from Newcastle to Barcelona has changed perceptions of him, with the England international feeling his technical and tactical qualities are finally receiving greater recognition.
Liverpool forward Cody Gakpo has returned to the club after withdrawing from Netherlands duty with an ankle injury sustained during their 2-1 Nations League victory over Serbia.
Norway have withdrawn Erling Haaland from Saturday's scheduled press conference ahead of Sunday's Nations League clash with Portugal in Oslo, following reports surrounding Manchester City's financial case.
Thomas Tuchel's concerns over Cole Palmer's repeated England absences remain relevant as the Three Lions look to recover from their 3-2 Nations League defeat to Spain.
