Williams said Fister had "no issues" Thursday.
Fister is on the 15-day disabled list retroactive to March 23 with a strained back muscle.
The plan is for Fister, acquired from Detroit in an offseason trade, to get five days' rest before increasing to three innings. He will then head to a minor league injury rehabilitation assignment for "probably a couple" starts, Williams said.
"We've got to build him like we would build him in spring. I think he's a little bit ahead of the game in that regard, but certainly would like him to get five innings somewhere, at least," Williams said.