Marcus is a speedy, tricky forward who can play out wide or through the middle both as a number 10 or striker. He had been earmarked for a big future by the club and travelled to the AEGON Future Cup in 2012 with the Manchester United Under-17 team despite being an Under-14 at the time. As an Under-16, he broke into the Manchester United Under-18 side in the 2013/14 season and made 17 appearances scoring 4 goals.
In the 2014/15 season, Marcus played almost exclusively as a centre forward due to injuries and the squad size. He finished the season with 13 goals. He made his Under-21 debut in September 2015 and was included as an unused substitute for the first team away to Watford in November 2015. Due to an injury to Anthony Martial in the warm-up against FC Midtjylland at home in February 2016, Marcus made his first start for the club and scored twice in the game. He followed that up with another double on his league debut at home to Arsenal.