San Francisco 49ers quarterback Jimmy Garoppolo went just 1-for-6 for zero yards and an interception on Monday night in his first game since he suffered a season-ending knee injury last September.

Garoppolo finished the night -- which ended with a 24-15 victory over the Denver Broncos -- with a 0.0 passer rating.

"Obviously [I'm] a little frustrated," Garoppolo said after the game. "But it's the NFL, unfortunately we don't get to play the whole game. ... You wish you could be out there for more so you could bounce back. ... It is what it is. It's the preseason right now, so you just gotta take it in stride."

Speaking on Tuesday, coach Kyle Shanahan said three rough series in an exhibition game weren't enough to cause concern.

"To get concerned over 10 plays or however many it was, that's pretty irresponsible,'' Shanahan said Tuesday. "You try to evaluate those 10 plays.''

Garoppolo's first pass was knocked down by defensive lineman Shelby Harris and his second one was intercepted by cornerback Isaac Yiadom when he was pressured by Bradley Chubb after a miscommunication by the offensive line.

"He got rid of it too early to avoid the hit and the route hadn't developed yet, so it didn't go far enough down the field,'' Shanahan said. "We need to do a better job in protection there by getting everyone on the same page and we need to do better at throwing that ball away, or if you can't, you have to take that sack.''

Garoppolo didn't fare much better on the second series when his first pass was tipped again at the line. Cornerback De'Vante Bausby then broke up a third-down pass that was nearly an interception return for a touchdown.

Chris Harris Jr. pressured Garoppolo into an incompletion from his end zone on his first pass of the third series before Garoppolo finally completed a screen pass to running back Matt Breida, who was corralled for no gain on the final pass of Garoppolo's night.

C.J. Beathard replaced Garoppolo in the next series.

``He got rid of it too early to avoid the hit and the route hadn't developed yet, so it didn't go far enough down the field,'' Shanahan said. ``We need to do a better job in protection there by getting everyone on the same page and we need to do better at throwing that ball away, or if you can't, you have to take that sack.''

The 49ers signed Garoppolo to a five-year, $137 million contract last year. After a promising start to the season, the Eastern Illinois product tore his ACL in a Week 3 game against the Kansas City Chiefs.

Garoppolo, however, didn't blame Monday night's performance on his knee.

"I wasn't thinking about it, so I was happy about that,'' Garoppolo said. "It didn't bother me too much.''

The Associated Press contributed to this report.