1949 NFL draft
On December 21, 1949 Halfback Doak Walker was selected as a “future pick” after his Heisman Trophy-winning junior season, but he stayed at SMU for his senior season in 1949. (He missed the 1946 season due to military service.) Walker’s draft rights were traded to the Detroit Lions, where his hall of fame career began in 1950
Sources:
https://en.wikipedia.org/wiki/1948_NFL_draft