"David's our starter," Del Rio told the Florida Times-Union.
The Jaguars drafted Blaine Gabbert with the 10th overall pick in April's draft and the rookie from Missouri started the Jaguars' first preseason game as Garrard recovered from a sore back.
Both quarterbacks struggled in Jacksonville's 15-13 preseason victory over the Atlanta Falcons on Friday.
Garrard completed 7 of 12 passes for 99 yards, with an interception in three series. Gabbert went 11 of 23 for 96 yards in seven series. Gabbert was plagued by several drops, including three on one second-half series that forced the Jaguars to settle for a 54-yard field goal.
The 33-year old Garrard threw a career-high 15 interceptions last season as the Jaguars missed the playoffs for the third straight year.
Information from The Associated Press contributed to this report.