Blaine Gabbert was the 10th overall selection in the 2011 NFL Draft.
Over three seasons in Jacksonville, he went 5-22 as the Jaguars' starting quarterback.
On Sunday against the Falcons, he will make his first start since Oct. 6, 2013.
What can 49ers fans expect to see?
"The one thing that Gabbert will do is he will play within some kind of rhythm and timing within the offense," Greg Cosell, Senior Producer at NFL Films said on KNBR 680-AM on Wednesday morning. "... He's a pocket quarterback at his core.