MacKinnon was selected by the
San Diego Chargers in the 33rd round (264th overall) of the
1962 AFL draft and the
Philadelphia Eagles in the 20th round (280th overall) of the
1961 NFL draft. As the last player selected in the
1961 NFL draft, he was designated
Mr. Irrelevant, however, he was the only such player ever to be selected as an All-Star, before Brock Purdy in 2024. He opted to sign with the
San Diego Chargers of the
American Football League to play as a
fullback. In
1966, he was moved to
tight end to take advantage of his blocking and receiver skills. Head coach,
Sid Gillman, employed MacKinnon with
Dave Kocourek in the first "twin tight-end" formations seen in professional football. He was on the Chargers' 1963
AFL Championship team in their victory over the
Boston Patriots. He was an
AFL All-Star in
1966 and
1968. In
1968, he averaged 19.6 yards per reception, posting 33 receptions for 646 yards and 6
touchdowns. On April 29,
1970, he was traded to the
Green Bay Packers in exchange for a future draft pick, but he refused to report and instead opted to retire. On September 15,
1970, he signed as a
free agent with the
Oakland Raiders, at the time part of the
National Football League. In
1974, he signed with the
Southern California Sun in the
World Football League to play
tight end. In 1976, he was a part of the initial four former players (along with
Emil Karas,
Frank Buncom,
Bob Laraba), that were inducted posthumously into the
San Diego Chargers Hall of Fame. ==Personal life==