Records of the Orange County (Fla.) Clerk indicate Fielder, 29, filed for divorce from his wife of eight years, Chanel, in May. They have made their off-season home near Orlando.
The ongoing divorce proceedings were first reported Wednesday on the blog Larry Brown Sports.
Fielder, the Tigers' first baseman, had seven home runs in April, but only 10 since, and just one since July 10, the Detroit News noted. He is batting .263 and has a .432 slugging average this season, career lows.
Teammate Torii Hunter came to his defense Wednesday during an interview on WMGC-FM, Detroit.
"Prince is a strong guy, man. He's out there every day, won't come out of the lineup. A lot of people don't know what's going on in his life, but this guy's a strong guy," Hunter said. "We (players) know what's really going on, and we appreciate him going out there."
The Fielders have two children, and renewed their wedding vows last winter, before Fielder signed the biggest contract in Tigers' history, the newspaper said.