After missing the entire 1963 season with a knee injury, Mertens returned as a reserve defensive back, playing a great deal at the safety position.

"[5] He remained one of the fastest players on the squad, clocked in pre-season running a 40-yard dash in full game gear in 4.9 seconds — tied for third best on the team.

[3] Although the torn ligaments in his knee were surgically repaired and he was able to rehabilitate his injury and come back in 1964,[8] he was not the same player and saw himself limited to reserve duty for all 14 games that year.

Right cornerback Abe Woodson had been traded away to the St. Louis Cardinals in exchange for running back John David Crow, opening up a place at the top of the team's depth chart.

[4] His action during the latter part of the season was limited by a pulled hamstring that he suffered in the November 7 game in the Cotton Bowl against the Dallas Cowboys.

[10] It was not until the final game of the season, at home against the Green Bay Packers, that Mertens was healed up well enough to return to the starting lineup.

[12] According to Mertens' brother, Bob, a total of 72 x-rays were taken to diagnose the injury, with doctors stating that if the break had been an inch or two lower, it might have proved fatal.

"[13] Twelve weeks later he was freed from the cast and fitted with a lighter brace, finally allowed to move his neck slightly.