ENGLEWOOD, Colo. --The idea of using Danny Trevathan and Brandon Marshall together as linebackers to wreak havoc in lateral pursuit was tantalizing It offered the Broncos a chance to have the league's most dynamic pair of linebackers in a nickel alignment.

But it's no longer meant to be -- at least not this season.

Monday brought the news that Trevathan's season is "more than likely" over because of a dislocated patella (kneecap) in his left knee -- the third injury to that knee since the start of training camp.

(NOTE: A day later, the Broncos placed Trevathan on injured reserve, officially ending his season.)

Trevathan suffered a medial tibial impaction fracture during training-camp practice Aug. 12, and missed the first three games of the regular season before returning Oct. 5 against the Arizona Cardinals. He endured a crack above the kneecap early in the Oct. 12 win over the New York Jets, and went to recallable injured reserve until Saturday, when the Broncos activated him.

"Danny's had a rough season as far as knee issues and sometimes setbacks are setups for better things to come," Head Coach John Fox said. "That'll be his mindset as he gets ready for surgery and then gets ready for the pretty strenuous rehab involved to come back. But we feel like he'll do a great job."

Exacerbating the loss of Trevathan is the foot sprain suffered by Marshall, who replaced Trevathan during the 11 games he missed to this point in the regular season. Marshall is considered "day-to-day," but foot sprains can be tricky; there can be a quick recovery, or it can take more time, as has been the case for Ronnie Hillman, who sprained his foot Nov. 9 and did not return to practice until the last two weeks on a limited basis.

When Trevathan left in the second half Sunday, the Broncos shuffled their linebacking corps. They briefly used starting middle linebacker Steven Johnson in the nickel, but settled on moving T.J. Ward back to his nickel linebacker role, which he handled for most of the previous five games, alongside rookie Todd Davis, who worked on the weak side.

The Broncos claimed Davis off waivers to fill the spot created when middle linebacker Nate Irving went on injured reserve Nov. 6 because of an injury to his medial collateral ligament.

Davis ascended during practice and in games on special teams, earning the opportunity when Marshall and Trevathan were sidelined Sunday.

"I felt really good," Davis said. "Right when I got here, everybody brought me in (and) treated me as their own. It felt real comfortable being in there."

The Broncos used 2014 draft picks Corey Nelson and Lamin Barrow in nickel roles when the need arose in October and November. But in San Diego, Davis, an undrafted rookie from Sacramento State, got the repetitions, to the delight of friends and family who drove from Palmdale, Calif., 164 miles away, to be there.

"I think [Davis] has adapted quickly," Fox said. "He does have good football awareness and football character. I think he's done a very good job in this short time."

Fox said it's "way too far ahead" to determine who would get the helmets with radio receivers next Monday in Cincinnati. Marshall and Trevathan wore them Sunday, and when both were out, the Broncos resorted to old-school methods to relay the defensive playcalls.

"It was interesting," Fox said. "You've kind of gotten away from signals on defense. But we had to readapt that. We kind of had a little system in place so we didn't have to signal. I don't want to get too much into that but it was actually without having to communicate visually with signals and without any kind of helmet communication. I thought our staff did a good job of adjusting to that."

"We kind of had to rely on talking more than ever," added Davis. "But I think it ended up pretty good."

Meanwhile, quarterback Peyton Manning and left tackle Ryan Clady will both be "day-to-day" with the thigh injuries that they suffered Sunday.

Manning missed only four snaps as a result of his injury, which Fox said could have been a result of dehydration after he became ill Saturday night and need four IVs between Saturday and Sunday in order to be ready to play against the Chargers.

Veteran Chris Clark replaced Clady, just as he did last year when Clady suffered a Lisfranc injury.

"I thought [Clark] did a good job," Fox said.

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