Mike Williams -- WARRANT ISSUED FOR BROTHER ... Allegedly Stabbed NFL Star

An arrest warrant has been issued for the brother of NFL star Mike Williams ... after cops say he stabbed the Tampa Bay Bucs wide out during an altercation in the player's Tampa home ... TMZ Sports has learned.

Officials say 26-year-old Williams was stabbed in the left thigh (above the knee) Sunday afternoon ... however they have not released information about the severity of the injury.

Cops tell TMZ Sports ... investigators spoke to witnesses and a warrant was issued for Eric Baylor for aggravated battery and domestic violence.

Williams -- who signed a $40 million contract with the Bucs last year -- was rushed to a nearby hospital where he's being treated.