Casares played professionally for the Chicago Bears and Washington Redskins of the NFL, and was a member of the expansion Miami Dolphins of the AFL.

[12] Casares was selected in the second round (eighteenth pick overall) of the 1954 NFL draft by the Chicago Bears,[13] but was offered a $20,000 annual contract with Canadian Football League's Toronto Argonauts.

[18] After ten seasons with Chicago, Casares was the Bears' all-time leading rusher with 1,386 carries, 5,657 yards, and forty-nine rushing touchdowns.

[19] "He was the toughest guy I ever played with," Mike Ditka, a former Bears tight end and coach, told The Tampa Tribune.

"[20] Casares was questioned in 1962 by NFL investigators as part of a spreading inquiry that included the FBI into links between league players and organized crime.

Casares, who had been seen with a bookie and was known to visit with other Bears players two nightclubs connected to the Chicago mob, said he had been questioned about point shaving for gamblers and had taken and passed two lie detector tests.

[21] The investigations eventually would lead to the one-season suspensions of Alex Karras, of the Detroit Lions, and Paul Hornung, of the Green Bay Packers.

Casares finished his professional career with the NFL's Washington Redskins in 1965, and in 1966 with the AFL's Miami Dolphins, receiving only limited carries in his final two seasons.

He died on September 13, 2013, at the age of 82, after a string of illnesses, including heart disease and shoulder problems stemming from his days in football.