Burton was a fourth-round draft pick in 2008 but struggled with knee injuries during his time in St. Louis. In 22 games with the Rams, including seven starts, he caught 38 passes for 425 yards and one touchdown.
The wide receiver missed the final seven games of the 2009 season after suffering a knee injury.
Spagnuolo talked about Burton the day after the Ravens game.
“Keenan is a pro,” Spagnuolo said. “He is what you want all your guys to be like on and off the field and in the meeting rooms and with the other players. Now, he’s had to battle some injuries, but he’s done it. That tells you a lot about the character of that guy.