Brethauer was a three year starter for the Oregon Ducks at end. He led the team in receiving and set a school record in catches all three years. Brethauer finished as the Ducks' career receptions leader with 101 catches. As a senior, he caught 41 passes for 486 yards and two touchdowns and was named second-team All-Pacific [Coast Conference].
Professional career
Brethauer was selected in the 24th round of the 1953 NFL draft by the Baltimore Colts. He caught 10 passes for 133 yards on offense and intercepted a pass on defense as a rookie during the Colts' inaugural season. Brethauer was drafted into the Army after the season and missed 1954 and was re-signed by the Colts after being discharged in 1955. Brethauer was waived during training camp in 1956.