The team announced Thursday that Spaeth has been released with the designation of failed physical.
"Matt never fully recovered from knee surgery that occurred this past offseason, and he will not be ready to return to football activities at this time," general manager Kevin Colbert said in a statement released by the team. "Matt played an integral role in our Super Bowl XLIII Championship run, and we wish him the best in his future endeavors."
Between the release of Spaeth and the offseason retirement of Heath Miller, Pittsburgh is undergoing a changing of the guard at tight end.
"You don't talk about tight ends (anymore). You're looking at either a Y or an F, and that's the way we talk about them," Keim explained. "You're either an inline guy who usually lacks the skill set to be a pass catcher. It's a tough overachiever that's physical at the point of attack. And then you have the guy who can flex and is essentially a big wide receiver. So the guy who can do it all generally doesn't exist anymore."