Huff left the team in New York over the weekend after struggling at the plate and in the field. The Giants originally said he had a family emergency.
Manager Bruce Bochy said on Wednesday that Huff is getting treatment for anxiety. He could rejoin the team in San Francisco over the weekend.
"He had an episode of anxiety," Bochy said, before a game against the Cincinnati Reds. "He got some treatment, he'll continue to get treatment. At this time, we thought the best thing was to make this move and put him on the 15-day disabled list."
The Giants called up infielder Joaquin Arias from Triple-A Fresno. He was in Cincinnati in time for the second game of a series against the Reds.
Huff has started four games in left field and six at first base. Huff was moved to second base for the first time in his career on Saturday because the Giants were short-handed, and he failed to cover the base on a potential double play, helping the Mets rally for a 5-4 win.
Huff also has struggled at the plate, going 1 for 15 in his last six games.
Bochy didn't know whether Huff has dealt with anxiety issues before now. When he left the team after Saturday's game, Bochy initially thought he might be experiencing a problem related to his on-field performance.
"I thought that was a possibility, yeah I did," Bochy said. "I didn't have a chance to talk to him, but we did pass some texts."