If sixth-round pick Ronald Johnson doesn’t make it in the NFL, one thing seems absolutely certain: It won’t be for lack of effort.

The Niners have raved about Johnson’s passion since they drafted the USC wide receiver, but they might have undersold his love for the game.

Johnson does more than eat, sleep and breathe football. He actually sleeps with his football.

In fact, Johnson said he takes his football everywhere. As I spoke with him today after the third day of the 49ers four-day minicamp, Johnson said his football, which he packed for his trip from Muskegon, Mich., was in his car.

He used to sleep with an NCAA football at USC, but he’s since switched to an official NFL ball. They’re the same size, but Johnson says they have a different feel.

Oh, another thing – he’s written something on his ball: Son.

“It sounds strange, but I have a relationship with the football,” Johnson said. “… I actually sleep with it. It sounds weird, but I do it. Just to get that extra edge everyone else doesn’t have.”

Johnson is all about finding an edge. Ever heard of athletes doing workouts to strengthen their … hip flexors? Johnson said he does those to increase his flexibility so he can “make the great catches” and, of course, “get the extra edge.”

Johnson said he’s routinely been up until 2 a.m. recently cranking out his daily regimen of 300 sit-ups and 300 push-ups (fingertip push-ups to strengthen his hands), studying his playbook (he said he’s written so many notes in it he can barely make out the plays) and playing with his football.

“I like to see how long I can play with it and not let it hit the ground,” he said.

Johnson will throw his football behind his back. He’ll toss it up, let it fall below his waist and practice snatching it by the nose with one hand – anything to make catching it become “second nature.”

He said he’s been constantly throwing a football to himself during practices this week. His teammates have noticed and today, he said, they threw five footballs at him, firing one after another. He caught them all, he said, smiling.

Johnson (5-10, 185), who was projected as a mid-round draft pick, instead fell to the middle of the sixth round, the 24th wide receiver off the board.

He said his disappointing draft experience has only increased his drive.

“It gives me a lot of fuel because I do things right,” he said. “I do what I have to do to be considered the best and I’m not considered up there right now. So I’ll keep doing what I have to do so I can be the best.”

• Johnson, who had a 10-day stay in the Bay Area earlier in the offseason, said he’s unsure if he’ll be staying after the minicamp to continue throwing sessions with quarterback Alex Smith and other wide receivers. He said Smith has paid for his plane tickets to the Bay Area.