Greenwood usually wears # 26 for United but wore # 7 as the United players returned to their home stadium for a run-out on Saturday.
United has stepped up preparations for a return to action in the Premier League with an intra-team friend to help build fitness after a three-month virtual absence from competition.
Greenwood posted a photo of the match, competing with Dan James, who highlighted the number on the back of his shirt.
United players in both teams wore the numbers one through 11, so it would be premature for fans to think it is an indication that Greenwood will inherit Alexis Sanchez’s number next season.
However, that didn’t stop United fans from splashing the image on Twitter.
Greenwood was recently praised by United teammate Jesse Lingard, who said Sky Sports: “He knows football, he shoots from the right foot to the left foot. Even today, I don’t know what foot it is. He can score free kicks with his left, take turns with his right. When given the opportunity, he shows what he can do.
“No matter the age, as long as you can play the day and do the work for the team, you will be on the team. He’s learning at a fast pace right now. “