The moved was announced on Sunday.
Jacksonville traded an undisclosed draft pick in 2010 to Tampa Bay on Saturday night in exchange for McCown. He is 1-6 as a starter, has completed 59.7 percent of his passes, and has nine touchdown passes and 10 interceptions. Byron Leftwich beat out McCown for Tampa Bay's starting job.
The Jaguars will head into their regular-season opener at Indianapolis next Sunday with little experience behind starter David Garrard and a backup still trying to learn the playbook.