"Last week, Adam felt his knee was giving him a little bit of a problem, so he had an MRI," Colts coach Jim Caldwell said. "They saw some loose cartilage in there, and we felt we wanted to get that done now with the bye week. In doing that, we had to look for someone to take his spot, and we found Matt Stover."
Losing Vinatieri, arguably the NFL's best clutch kicker, for four to eight weeks is one thing. He missed training camp after having surgery on his right hip and right knee this summer, and though Vinatieri was still hurting last weekend, he managed to make a short field goal during the fourth quarter of Sunday night's 31-9 rout of the Tennessee Titans.
Cutting Johnson was an entirely different matter.
He now has been released twice in the past 13 months by the Colts, the first coming in September 2008 after Johnson was arrested on a drug possession charge. He re-signed with the Colts in May as the team tried to beef up its undersized defensive line, and the third-year pro won back his starting job in camp.
The difference from last season is staggering. A year ago, the Colts finished among the bottom third of the league against the run. This year, they are 14th.
But after Wednesday's practice, Caldwell ended speculation that Johnson, who also had a checkered career at Penn State, had run into more problems off the field. Instead, Caldwell said, Johnson wasn't performing well enough to keep the job.
Johnson had started four consecutive games after serving a one-game suspension in Week 1 because of his arrest and had nine tackles.
The two moves are the latest obstacles that Indianapolis faces.
The Colts are 5-0 for the fourth time in the last five years despite having a new head coach, a new defensive coordinator, a new special teams coach and no Marvin Harrison. Safety Bob Sanders, the 2007 NFL Defensive Player of the Year, still hasn't played, and other injuries forced the Colts into starting two rookie cornerbacks at Tennessee.
Even the durable Peyton Manning gave fans a scare, saying he needed postgame treatment on his left knee Sunday night. Manning said he hurt the knee late in the first half against Tennessee on a play in which Titans defensive end Kyle Vanden Bosch was called for roughing the passer. The MVP quarterback went through a full practice Wednesday and said the knee was fine.
"No concerns," he said. "It feels fine. It's a non-issue."
Vinatieri's knee, apparently, is an issue.
Stover, a 12th-round draft pick of the New York Giants in 1990, played with Cleveland from 1991 to 1995, then moved with the team to Baltimore in 1996, where he spent the next 13 seasons.
"That Adam would continue to kick with his knee in that condition, it tells you what kind of guy he is," Stover said. "What I pride myself on is getting out there and making all of my field goals."
Sanders, who was held out of practice until last week, was a limited participant in Wednesday's practice, though he did have his most extensive work.
Cornerback Kelvin Hayden also practiced after missing the last three games with a left hamstring injury and has said he plans to return to the lineup Oct. 25 at St. Louis.
Anthony Gonzalez, who hasn't practiced since spraining ligaments in his right knee during the Colts' season opener, has started running again, though it's not clear when the wide receiver might return to the field.
The Associated Press contributed to this report.