The England striker waged a high-profile campaign last year to persuade the British government to extend free meal vouchers to vulnerable young people throughout the summer school holidays.
Ole Gunnar Solskjaer made a change to the team's formation, switching from a 4-2-3-1 to a 3-4-1-2, the side led by a strike partnership of Cristiano Ronaldo and Edinson Cavani.
United defeat Spurs 3-0 at the Tottenham Hotspur Stadium on Saturday to move to fifth place in Premier League standings. The side now has 17 points from 10 matches.
Marcus Rashford was last seen on a football field missing a penalty for England in the shootout loss to Italy at Wembley Stadium.
The Premier League club, which kicks off the new season in just over two weeks, did not specify how long the 23-year-old Rashford could be out.
The government plans to add online racism to the list of offenses for which fans can be barred from matches, UK Prime Minister Boris Johnson said.
After England lost the finals of Euro 2020 against Italy, the mural of striker Marcus Rashford was vandalised.
Football Association condemns racist abuse of players after England's defeat to Italy in Euro 2020 final
The England football team felt disgusted when the players were subjected to discriminatory abuse on social media following the Euro Cup final loss.
Southgate's strategy will be analyzed for years to come in a nation still waiting for a first major title since the 1966 World Cup.
Manager Gareth Southgate has been able to regularly change his team, with a plethora of attacking talent at his disposal.
The conversation will be released in full on Penguin UK's YouTube channel at 1300 GMT on Friday.
English football clubs and players boycotted social media for four days in April and May to protest against racist abuse and push for more action from the companies which run the platforms.
Marcus Rashford on Saturday named both Wayne Rooney and Cristiano Ronaldo in a dream Manchester United six-a-side team.
Marcus Rashford was lively on the ball, happy to come deep to kick-start moves and used space cleverly all evening.
A spat between the England camp and the British media erupted earlier this week after photographs apparently showed Southgate's assistant carrying the team selection for Sunday's Group G clash.