Mason Greenwood has added significant muscle to his frame during the break from Premier League action.The 18-year-old is enjoying a breakthrough season under Ole Gunnar Solskjaer, scoring 12 goals in 35 appearances this season, though he's made just four starts in the Premier League.United are back in action on Friday as they travel to London to face former manager Jose Mourinho's Tottenham side, with both teams vying for a place in the top four.