Before the 49ers’ first training-camp practice on Thursday, we’ll be examining some key questions. First up: Their backup quarterback ….

As with most NFL teams, the 49ers’ season will be sunk if their starting quarterback sustains a serious injury, right?

Perhaps. But they hope they purchased quality Colin Kaepernick insurance in March when they traded for Jaguars quarterback Blaine Gabbert.

Jacksonville fans, of course, will scoff at the suggestion Gabbert could serve as reliable fill-in if Kaepernick is sidelined for the first time in his 29-start career. After his first three seasons, Gabbert has the third-lowest completion percentage (53.3) and passer rating (66.4) among the 93 quarterbacks who have thrown at least 700 passes since 2000.

A hopeless case? It’s perhaps telling the Jaguars dealt Gabbert, the No. 10 pick in 2011, to the 49ers for a sixth-round pick (No. 205).

For their part, the Niners hope Gabbert’s union with Jim Harbaugh will allow his career to follow an Alex-Smith-like trajectory.

And Gabbert, who is scheduled to earn a $2.01 million base salary, figures to have plenty of opportunities in the preseason to suggest he could still flourish. Last year, Kaepernick was mostly a rumor in four exhibition games: He directed six drives and had 23 pass attempts.

In 2013, the 49ers traded for Colt McCoy to serve as Kaepernick’s backup and his desultory preseason performance (52.6 rating) helps explains why they didn’t re-sign him in the offseason. Thanks to Kaepernick’s durability – he missed 22 snaps — McCoy threw one regular-season pass, meaning it’s not known if he could have been a serviceable starter.

A year later, the 49ers have moved on to Gabbert. Can he save a season if Kaepernick is hurt?

The 49ers hope that question will remain unanswered.

*************************************************

For those who took the offseason off, here’s a feature on Gabbert from April. Said NFL Network analyst Kurt Warner of the 6-foot-4, 235-pound Gabbert: “There’s enough physical tools there, but I think most guys that get to this level have the physical tools. I think what separates guys is their mental ability to go beyond that. Those are the things that I haven’t seen develop in Blaine to the point where I say, ‘This guy is an NFL starter.'”