Sancho, 23, is training away from United's first-team after saying in a now-deleted statement on social media that he had been made a "scapegoat" following his omission from the squad for the 3-1 defeat at Arsenal on Sept. 3.
Manchester United collected a third straight win in the Premier League with a first-half Jadon Sancho goal giving them a 1-0 win over Leicester City at the King Power stadium on Thursday.
The winger suffered a minor knock during a training session earlier this week and he was forced to miss his team’s 4-0 win over Hungary in Budapest.
Bayern are ten points clear at the top of the league and an away win at Mainz will guarantee the title with three games remaining.
Sancho, a product of City's academy, rejected a new contract at the Premier League club when he was 17 to join Dortmund in 2017.
Haaland continued his prolific run in the Champions League by scoring twice as his side came from behind to earn a 3-2 win at Sevilla.
Sancho says his form has dipped slightly this season but dismissed suggestions that it is due to media speculation about his club future.
United, who booked a place in the Cup quarter-finals with a 3-0 win over Brighton & Hove Albion on Wednesday, host Tottenham Hotspur in the league on Sunday.
In-demand winger Jadon Sancho says he is happy at Borussia Dortmund and is enjoying helping some of the younger players develop at the Bundesliga club.
POOL/AFP / Lars Baron
Two times Champions League winner, Hargreaves, urged the big European clubs to come and sign Sancho in the summer transfer window.
The 18-year-old has also featured regularly in the Champions League, making 28 appearances in all competitions this season.
The 18-year-old came on for Raheem Sterling in the Nations League game in Rijeka played behind closed doors.