Multiple outlets reported that Matz is dealing with a nerve problem in his elbow. The 26-year-old had a shot on Monday and could be in need of surgery.
"This is not an injury," Collins said. "It's just an issue of ... he needs to shut it down for a little while. If he had to, he could pitch tomorrow."
As it stands, Matz was scheduled to pitch Tuesday against the Arizona Diamondbacks, although fellow left-hander Tommy Milone appears likely to get the nod instead.
Matz began the season on the disabled list and has been struggling since his return, posting a 2-7 mark with a 6.08 ERA. He is 0-6 with a 10.19 ERA in his last eight starts.