Day was selected in the 1st round (8th pick) by the Milwaukee Bucks in the 1992 NBA Draft. He was joined in the first round by teammates Oliver Miller and Lee Mayberry, giving the Razorbacks three first round selections that year. He was traded with Alton Lister to the Boston Celtics for Sherman Douglas on December 22, 1995. Day scored a career high 41 points against the Minnesota Timberwolves, tying Larry Bird's Celtic franchise record for points in a quarter with 24.