Johnson missed two games with the knee injury, but still caught 84 passes for 1,492 yards and 12 touchdowns this season.
"He played the entire season with a finger really that was pointing perpendicular from his body the whole season," Mayhew said, via DetroitLions.com. "He's trying to catch the ball like that. He would never complain about that, but certainly that was a factor, I think, in the way he played."
Johnson reportedly was dealing with PCL sprain for most of the season, but Mayhew said that the surgery wasn't related to that.
"No, it was just a minor scope. He's going to be fine," Mayhew said.
Johnson, 28, became the first receiver to rack up 5,000 receiving yards in any three-year span.