The 27-year-old had been experiencing soreness in the back of his right shoulder since his last outing on Tuesday against the Twins. After briefly throwing on Saturday, Niemann decided it would be in his best interest to skip one start in the rotation.
"It's just been sore," Niemann said. "It's been getting significantly better each day, and it's at a point where I'd rather take the improvements I've made these past few days and not go out and push it and fall back to square one."
Manager Joe Maddon noticed in Niemann's last outing that the big right-hander's control was not as sharp as it has been in the past. Niemann, who issued two walks, a single and a home run in the game's first inning, settled down to throw seven innings. The 27-year-old has pitched 141 1/3 innings in just his second full season in the big leagues.
"His command has been off a bit for a while," Maddon said. "It's kind of unusual to watch under those circumstances, because he's the one guy that I've always talked about among everyone on our staff having the most consistent and best command of our group. On top of that he throws the largest variety of pitches -- fastball, curveball, slider, cutter and split -- [which] he's always been really good about.
"I'm sure it's something that he'll work back through, but it's been kind of unusual to watch."
Right-hander Andy Sonnanstine will make the spot start in place of Niemann on Sunday. Sonnanstine was activated from the 15-day disabled list with a strained right hamstring on Saturday, with Dale Thayer being optioned back to Triple-A Durham. It will be his first Major League start since Sept. 16, 2008.
"With Sonny being here coming off the DL that was not the original plan at all, not the concept," Maddon said. "We were just kind of lucky in the sense that he was here and able to start a game tomorrow. Also that had an impact today regarding the bullpen usage and how we were able to do that."
Despite pitching 1 1/3 innings with Class A Advanced Charlotte on Thursday, Maddon said he has no hard pitch count for Sonnanstine, hoping to get five solid innings.