To make room on the roster, outfielder Abraham Almonte was optioned to the alternate training site.
Hosmer was placed on the IL on Aug. 1, retroactive to July 29. He was scratched from the lineup three previous games.
"I'm feeling a lot better," he said Saturday. "I'm feeling like I'm getting a lot of my strength back, gaining a lot of the weight I lost. Feels good to be back, being able to do something with the guys."
Hosmer said he never received a precise diagnosis of the ailment and plans to see specialists after the season.
The team said it was not related to COVID-19.
"I went a couple weeks there struggling to get fluids down, nutrients down," Hosmer said. "I've been on a pretty consistent schedule now as far as eating."
He has yet to hit a ground ball. He hit a pair of bases-clearing doubles in a 7-2 victory against Arizona in the season opener and a home run in a loss to the Diamondbacks two days later.
He was back at first base and batting fifth against the Arizona Diamondbacks on Saturday night. Rookie Jake Cronenworth, who made seven starts at first during Hosmer's absence, started at second base and hit seventh. Cronenworth has been impressive with his bat and glove.