ENGLEWOOD, Colo. -- Denver Broncos quarterback Drew Lock enters Week 8 in a struggling offense. The Broncos are ranked 28th in total offense and scoring offense. Lock is last in the league among qualifying quarterbacks in completion percentage, passer rating, passing yards and touchdown passes.

In what was supposed to be his first full season as the Broncos' unquestioned starter at quarterback, he's missed two games and half of another with a right (throwing) shoulder injury.

Fans in Denver have begun to grumble. As the Broncos face Los Angeles Chargers rookie quarterback Justin Herbert for the first time this Sunday (4:05 p.m. ET, CBS), Lock will be under the microscope.

Fair or not, here it comes.

"When you play quarterback, you are going to get criticized regardless," Lock said this week. "I've been criticized plenty of times at the University of Missouri. It just is what it is. It's what we signed up to do, but this is also what we love to do."

Which brings us to Herbert. The Broncos have the same record as the Chargers at 2-4, but Hebert has made a significant splash with three 300-yard games in five starts. He has 12 touchdown passes and three interceptions, none in the past two games. Conversely, Lock has no 300-yard passing games and has thrown one touchdown with four interceptions this season.

Herbert has chucked it deep -- a gaudy 8.4 yards per pass attempt -- run for two touchdowns and played so well that Chargers coach Anthony Lynn had to keep him in the lineup even when Tyrod Taylor, who started the team's opener, was ready to return from a punctured lung.

"You can definitely tell he believes in himself and I feel like that's half the battle," Broncos linebacker Malik Reed said of Herbert.

Lock helped the Broncos finish 4-1 over his five starts last season, a stretch that included his 309-yard day in Houston last December. But this season he has often deferred on easy and available completions -- especially in Sunday's loss to the Kansas City Chiefs -- in favor of riskier throws downfield that largely haven't paid off. At a time when 28 quarterbacks in the league are completing at least 60% of their passes, with five over 70%, Lock is currently at 55.9% and hasn't thrown a touchdown pass since the season opener.

"When we play a defense like the Chiefs -- they played big zones against us and forced me to check it down," Lock said. "... They were forcing me to check it down and I wasn't doing it. I was running around and, in return, forcing balls down field a little bit. It ended up hurting our offense and it took us off the field. I can be a lot better than that, and that's a big goal of mine this week.

"I missed a couple of baby throws, those that I made in Pop Warner, and that's unacceptable by me. ... I'm working on that not happening again."

With the 25-year-old Patrick Mahomes in Kansas City already an MVP and Super Bowl champion and Herbert garnering praise for his early season work, Lock is suddenly the young prospect in the division facing the most questions, something that wasn't true when the season began eight weeks ago.

But it's not all on him. The Broncos continue struggle under their fifth different offensive coordinator in the past five seasons and with their top wide receiver (Courtland Sutton) on injured reserve. Their continued attempts to have Lock, and the other two quarterbacks who started in Lock's absence (Jeff Driskel and Brett Rypien), play out of three-wide receivers sets -- they've played it on 60% of their snaps -- has brought little reward and plenty of trouble.

In three-wide sets this season, Broncos quarterbacks have been sacked 13 times (72% of the season total) and have been intercepted 10 times (100% of the season total). In all, the team has scored three touchdowns while playing it, and this week coach Vic Fangio acknowledged the difficulties.

"Some of those times you're in those groupings because of the situation, whether it be third down, whether you're trailing, etc.," Fangio said. "I know we've played more three-wides than the other groups, so the numbers will be higher, but you make a good point. We've had too many negative plays in that personnel group."