Coach Bruce Arians told SiriusXM NFL Radio on Tuesday night that Johnson's stubbed digit, which caused him to miss last week's 13-10 win over the Tampa Bay Buccaneers, got worse before Johnson was pulled from practice last week.
"There was a slight infection after the first hit, when they had the cast on," Arians said, per Fox Sports.
Arians blamed the infection on the cast that Johnson wore and said the safety is being fitted with a new one.
"There's no telling what germs you're trapping in there when you ball it up and put the cast on," Arians said. "The stitches are still there. He could evidently lose more of the digit if he bangs it too much, and with any infection they could have to take more off. We're going to be careful with it."
With Tyrann Mathieu taking over the starting safety job, there is no need to push Johnson onto the field. Mathieu has displayed superb playmaking ability and ball skills to complement strong safety Yeremiah Bell.
It was only a matter of time before Mathieu took over the starting role. Johnson's unfortunate injury just sped up the process.