Gabbert threw deep to rookie wide receiver Justin Blackmon in coverage, but the ball was picked off:
"It was just a terrible throw, terrible decision. I tried to get a big play, but that's inexcusable," Gabbert told reporters after the game. "I've got to trust my progression and find the open guy. It's pretty simple."
Gabbert finished the day 27-for-38 for 220 yards, two touchdowns and two interceptions.
The Lions won the game, 31-14. Detroit opened up a 21-0 halftime lead. All of the Jaguars' points came in the fourth quarter.
Jaguars head coach Mike Mularkey said Gabbert threw a post into coverage and that's something "you don't want to do. Lesson learned."
Gabbert said there was a 50-50 chance Blackmon would come down with the ball, "but it's my job as a quarterback not to throw that post."
Jacksonville doesn't have much time to shake off the loss to Detroit. The Jaguars host the Indianapolis Colts on Thursday night. The Jaguars' only win of the year came against the Colts, 22-17, on Sept. 23.