It was evident on Wednesday night in Miami's 7-1 loss to the Phillies. Johnson gave up six runs on 11 hits in 3 2/3 innings.
The hits allowed were a career high, and a sign that the two-time All-Star is lacking the touch to put hitters away.
"I don't think it's as bad as it looks," pitching coach Randy St. Claire said on Thursday.
Johnson is working on some mechanical adjustments with his hands. Otherwise, the right-hander continues to go through his regular routine, working on regaining his old form.
Johnson missed most of 2011 with shoulder inflammation, and he's shaking off the rust.
His velocity is in the 92-93 mph range, with an occasional 94, down from the 95-97 of a year ago.
The feeling around the team is Johnson's velocity will increase as he keeps building up arm strength.
In the meantime, Johnson is laboring to get back to his elite status. In his two starts, he's allowed 21 hits in 9 2/3 innings. It's a dramatic reversal from last April, when he gave up 18 hits in 41 innings and he was 3-0 with a 0.88 ERA.
He's also lost two straight starts for the first time since June 18-29, 2007, when he dropped three in a row.
Johnson on Wednesday also was hurt by some sloppy plays in a five-run third inning. There was an error and some throws to wrong bases.
"We made some plays that shouldn't have been made," bench coach Joey Cora said. "We made some throws that shouldn't have been made, but [Johnson] wasn't sharp, either. They played better than we did. It's that simple."