Danario Alexander has performed well at receiver for the Chargers since signing late last month.(US Presswire)

The Chargers (4-5) are trying hard not to define this Sunday’s game against the Broncos (6-3) as a must-win. “Every week is a must-win,” coach Norv Turner and several players said with eerie similarity, as if they had rehearsed their answer.

If San Diego loses, it will fall three games behind Denver in the AFC West with six to play. The Broncos would also own the tie-breaker. Therefore, the actual deficit would be four games.

The Chargers have not beaten a team with a winning record this season and they have three remaining on their schedule (Broncos, Ravens 7-2, and the Steelers 6-3). Nevertheless, the always optimistic QB Philip Rivers believes the Bolts can make a late-season run. “We are going to keep fighting,” Rivers said. “We have been in worse positions than 4-5 and two games back with a chance to cut it to one.”

Alexander for now:  WR Danario Alexander, who was signed on Oct. 22, received the start last Sunday against Tampa Bay in place of a struggling WR Robert Meachem. Alexander caught five passes for 134 yards and a TD. He now has eight receptions for 195 yards in two games. Meachem has only 13 receptions for 197 yards and two TDs in his eight games.

Alexander will likely see a lot more opportunities than Meachem as long as he continues to perform well. Turner indicated both would receive playing time moving forward. “I think we can use all of our receivers,” Turner said. “It’s a matter of matchups. The guys that give us the best opportunity to make plays ... the guy who has the hot hand. Obviously, Alexander has had back-to-back nice performances.”

Mathews sidelined: RB Ryan Mathews did not practice Wednesday due to a stiff neck. The injury occurred when Buccaneers LB Quincy Black led with his head as he tackled Mathews. Black injured his neck on the play and was strapped to a board, carted off the field and taken to a hospital for evaluation. Black was later released and is expected to make a full recovery, but was placed on the season-ending reserve-injured list Tuesday.

Mathews is expected to practice later in the week and play Sunday. He will be needed. Three of the five 100-plus rushing performances Mathews has had in his career have come in the five games he has faced the Broncos.

Mathews rushed for only 74 yards in Week 6 against Denver. Turner inexplicably went away from Mathews, despite having a 24-0 halftime lead, and the Broncos came back to win 35-24.

Gaither saga continues: LT Jared Gaither (groin), who is frequently injured, missed practice Wednesday. Including last week, Gaither has missed five games this season and his prognosis for playing this week looks bleak. “He wasn’t able to practice today,” Turner said. “That’s where he is at. “When he is able to practice and I can watch him practice and he is able to move around, I will give you an update in terms of being able to play.”

Brown runs: WR Vincent Brown ran sprints on the side field for the first time since he broke an ankle in the second preseason game. Brown was the first player in the NFL to be placed on the new reserve-injured; designated to return list and is expected to play this season. Now that Brown is running, his return may be three to four games away, but a timetable has not been given.

Practice squad shuffle: WR Tori Gurley was released and DT Charlie Bryant was re-signed.

Practice report: OLB Antwan Barnes (hamstring), NT Aubrayo Franklin (Knee), LT Jared Gaither(groin) and RB Ryan Mathews (neck) did not practice. SS Atari Bigby (quad) and P Mike Scifres (ankle) were limited. CB Chris Carr (knee) LG Tyronne Green (ribs) and OLB Melvin Ingram (knee) full-participated. Barnes, Franklin, Mathews, Bigby, Scifres, Green and Ingram were new additions to the list following Sunday’s game.

What’s next: The Chargers will practice in pads Thursday.

Follow the Chargers and Dan McLellan on Twitter @CBSChargers and @sandiegosports.