"He has been dismissed for a violation of team rules," Fisher said. "We wish him the best in everything he does. We love him."
Sources close to the situation told ESPN.com that Fortson was dismissed for multiple failed drug tests.
Fortson could not be immediately reached for comment Sunday.
"He's a very good player," Fisher said. "As he became more consistent he became a good player."
Fortson, a junior from Hurtsboro, Ala., was the Seminoles' third-leading receiver last season, finishing with 45 catches for 610 yards with four touchdowns. He was expected to be one of quarterback Christian Ponder's biggest weapons this coming season.
Sophomore Rodney Smith probably will take Fortson's spot on the depth chart although he had only one catch last season.
"I think he's ready for it," Fisher said. "He's had some good practices."
It is the second loss of an expected impact starter for Florida State, which is starting its first season under Fisher following the retirement of Bobby Bowden.
Last month, linebacker Nigel Carr was arrested on five criminal charges, including two felonies. Carr, who was named the team's most dependable linebacker during the spring, has been indefinitely suspended from the team.
Mark Schlabach is a college football reporter for ESPN.com. Information from The Associated Press was used in this report.