Randy Johnson is progressing well in his rehabilitation from back surgery, but the Diamondbacks still aren't sure when the Big Unit will be ready to pitch in a spring training game. Johnson is scheduled to play catch on Saturday and pitch to hitters again soon after that, manager Bob Melvin said before the Diamondbacks' game against the Athletics on Friday night. Melvin said the team would then try to determine when Johnson would be ready to pitch in a game. Melvin is pleased with Johnson's recovery from the October operation and said there have been no setbacks.