Gabbert was Jacksonville's first-round pick -- and 10th choice overall -- in the 2011 NFL draft after playing collegiately at Missouri. The Tigers were 18-8 with Gabbert as the starting quarterback.
He is expected to be a backup to David Garrard this season, but Garrard left the Jaguars' practice last week with back problems. De Rio termed the injury as "nothing major."
Jacksonville has its first pre-season game Thursday at New England.