1:33 PM PT -- TMZ Sports obtained court docs explaining the allegations ... and they're graphic and disturbing.

The accuser is a male family member who claims Wetteland engaged in oral sex with him on 3 separate occasions between 2004 and 2006 ... while he was a young child.

Wetteland has been booked for 1st degree felony continuous sex abuse of a child -- and if convicted, he faces up to LIFE in prison.

John Wetteland -- the former closer for the New York Yankees -- was arrested in Denton County, Texas on Monday on suspicion of child sex abuse ... official records show.

Details surrounding the alleged incident are unclear -- but the charge specifies that the alleged victim is under the age of 14.

The 52-year-old right-hander was booked and posed for a mug shot. He was later released on $25,000 bond.

We're reaching out to law enforcement to find out more.

Wetteland was a star back in the day -- he was the MVP of the 1996 World Series, helping his Yankee squad defeat the Atlanta Braves. He posted all 4 saves for the Yanks during that series.

He was also a 3-time All Star during his 12-year MLB career ... during which he played for the Dodgers, Rangers and Expos.

During his Yankees career, Mariano Rivera was his set-up guy.

He later went on to serve as a bullpen coach for the Washington Nationals.

Story developing ...