[1] He became a star football player at Cuero High School, and was selected to the Houston Post's All-Southeast Texas Class B team in his junior and senior years.
[1] Mayne, who was nicknamed "Mugge" in high school, played in a North-South Texas all-star game at the end of his senior season.
Cuero reached the regional playoffs that year, but lost 19–10 to Junction High School despite a 15-yard field goal and 95-yard touchdown return by Mayne.
[1] After graduating, Mayne enrolled at the University of Texas at Austin, where he played football and ran track and got the nickname "Mickey".
[1] He was sent for training to Lincoln Air Base in Nebraska and played on the station's service football team, the Wings.
[1][2] Mayne again entertained an offer to play for the Bears in 1947, and agreed to switch leagues after talking to team owner George Halas.
[2] Mayne did not play in the first few games of the 1947 season because of injuries and an infection, but head coach Paul Brown made him the starter at right halfback in October.
[2] He suffered a separated shoulder during the season, and was bothered by a two-year-old injury that turned out to be a bruised spinal cord.