SANTA CLARA, Calif. — With a bye this week, the San Francisco 49ers have time to regroup, especially up front.

The 49ers’ offensive line took another step backward in Denver on Sunday night, a reflection of the direction the unit has been pushed by the opposition — and its own injuries — this season.

On a night when the sometimes seemingly unsackable Colin Kaepernick was put on his back a season-high six times, the worst news came after the 42-17 debacle in Denver when starting center Daniel Kilgore was diagnosed with a broken leg that will require season-ending surgery.

The injury came on a night when the 49ers got twice-injured right tackle Anthony Davis back in the lineup. With star guard Mike Iupati expected to return from his concussion for the club’s next game — Nov. 2 against the St. Louis Rams — brighter days for the offensive line appeared to be on the horizon.

But now down goes Kilgore, to be replaced — apparently — by a guy who has never played an NFL regular-season game, Marcus Martin.

“Right now the first shot at (replacing Kilgore) is going to be Marcus Martin,” coach Jim Harbaugh announced Monday, a day that began the 49ers’ bye week.

Martin, the 49ers’ third-round draft pick last spring out of USC, suffered a dislocated kneecap against the San Diego Chargers in the preseason. He has yet to be active for a game.

Harbaugh said he’s seen enough of Martin at practice to be confident he can step right in.

“He’s excelled at the mental aspects. I’ve been real impressed with that,” the coach said. “Even when he knew he was hurt, knew he was going to be out multiple weeks, he did not ease off in terms of the classroom and the study. I think that bodes well.

“Bright youngster and he’s champed at the bit to get back on the field and didn’t take the opportunity to let the injury linger. So, good signs. Excited about his progress, and I look forward to good things.”

It isn’t as if Martin should not be expected to do well. He was rated by NFLDraftScout.com as the second-best center in the draft and certainly would have seen more playing time if it weren’t for the kneecap injury.

He was projected as a second-round pick by NFLDraftScout.com, which described him as “a thick plugger who has plenty of strength but doesn’t seem to be the brute you expect. Does not necessarily fire out and consume defenders but uses his girth to effectively wall them off or barge through to create a wide running lane. Tweaked his knee in November, didn’t run at the combine, then ran 40 yards at pro day with a disappointing best of 5.52 seconds. “

–The 49ers hope Iupati and standout linebacker Patrick Willis will be fully up to speed by the time the club returns from the bye.

Iupati had to sit out Sunday’s 42-17 loss to the Denver Broncos because he hadn’t passed the league-mandated protocol for players who have suffered concussions. The fact that the 49ers had a short week following a Monday night win in St. Louis handicapped Iupati’s ability to prove his head had cleared in time to face the Broncos.

Willis’ situation is a bit more up in the air. He suffered a toe injury in the win in St. Louis and could not practice last week. The injury was not deemed serious, and a second week of inactivity could be sufficient in order for Willis to get back on the practice field leading up to the rematch with the Rams.

REPORT CARD VS. BRONCOS

–PASSING OFFENSE: D — The 49ers knew they were in the unenviable position of taking a banged-up defense up against Peyton Manning on Sunday night. So they were hoping they could win a shootout in Denver. Clearly, they couldn’t. Kaepernick attempted a season-high 39 passes and threw for 263 yards, his second-highest figure of the season. But hounded all night by the Denver defense, and sacked a season-high six times, Kaepernick was far less effective than his yardage total might indicate, offsetting one touchdown with one interception and recording his second-worst passer rating of the season, 79.3.

–RUSHING OFFENSE: F — Missing their best run blocker with G Mike Iupati out with a concussion, the 49ers gave up on their running game almost immediately in Sunday’s loss at Denver. They ran the ball only 15 times, as compared to Colin Kaepernick’s 39 passes (and seven more from backup Blaine Gabbert). Frank Gore (nine rushes, 20 yards) wasn’t given much of a chance, and backup Carlos Hyde (three rushes, 15 yards) got even less of one.

–PASSING DEFENSE: F — The 49ers were on the field for Manning’s record-breaking touchdown pass Sunday night. That had as much to do with the schedule as anything else. What could have been avoided was Manning’s near-perfect, 22-for-26 success rate for 318 yards on a night when the 49ers had hoped the return of top corner Tramaine Brock would help slow the record-setter. Manning was so unstoppable, the Broncos felt sorry for the 49ers and gave him the fourth quarter off.

–RUSHING DEFENSE: D-minus — The fact that the Broncos were able to build a big lead with Manning passing against an injury-plagued secondary wasn’t a big surprise. What was most disappointing was the way the Broncos were able to grind the clock in the second half with their running game. Backup Ronnie Hillman had more rushing yards (74) than the 49ers (53), and he added two back-breaking touchdowns. The Broncos totaled 113 rushing yards on just 22 carries.

–SPECIAL TEAMS: B-plus — A poor offensive showing meant more opportunities for punter Andy Lee, and he took advantage. He boomed a 71-yarder among five kicks that averaged 54.4 yards. Lee’s teammates did him proud as well, limiting the Broncos’ return opportunities and allowing Lee to record a 50-yard net average. Phil Dawson failed to take advantage of the light-air conditions, missing a 51-yarder wide left.

–COACHING: C — Other than maybe try to run the ball more often, there really wasn’t much the 49ers’ coaching staff could do with a depleted roster going up against an elite team in the blowout loss to Denver. It’s hard to blame the coaches when the other team takes advantage of key injuries in the offensive line to record six sacks and a severe shortage of healthy players in the secondary to celebrate Manning’s historic night.