The past seven days for the San Francisco 49ers have been rough.

A defeat to an Arizona Cardinals team missing Kyler Murray, DeAndre Hopkins, A.J. Green and J.J. Watt ensured the Niners would enter Week 10 with a sour taste in their mouth having fallen to 3-5 on the season.

In a game viewed as a golden opportunity for the Niners to put themselves firmly in the playoff picture, they produced one of their worst performances of the year, and most expect their profligacy in failing to take that chance to be punished further against the Los Angeles Rams on Monday Night Football.

San Francisco's mood going into a contest with a Rams team also smarting after throwing in a clunker against the Tennessee Titans will not have improved with the news that came down on Thursday when Los Angeles signed three-time Pro Bowl wide receiver Odell Beckham Jr. following his release by the Cleveland Browns.

Beckham is expected to make his debut at Levi's Stadium, where edge rusher Von Miller could also make his Rams bow having landed with Los Angeles in a trade from the Denver Broncos on November 1.

It is Beckham and Miller who will grab all the pre-game attention as the Rams look to pile the misery on the 49ers and improve to 8-2 in their bid to win the Super Bowl at their home stadium in February.

However, it is how each team deals with their absentees, rather than the performances of Beckham and Miller, that is likely to decide a potentially high-scoring matchup out west.

How will Woods loss impact run game?

The addition of Beckham initially appeared to be a luxury one for the Rams, whose receiver depth allowed them to recently part with veteran DeSean Jackson.

Yet, a day after Beckham's arrival, his signing was revealed as a much more necessary move with the news Robert Woods had suffered a torn ACL, ending his season.

Woods has long since been an integral part of the Rams' offense, not just for what he does as a receiver but also for his impact in the blocking game.

Per Stats Perform data, Woods' had an adjusted run-block win percentage of 88.89, the wideout comfortably outperforming the average for tight ends and fullbacks of 71.48.

The Niners rank 19th in opponent rush average allowed, giving up 4.37 yards per carry, but the Rams may struggle to take advantage of that fragility if they cannot replace Woods' influence in that regard.

With D.J. Jones (56.70), Nick Bosa (40.04) and Arik Armstead (48.84) all above average in double-team adjusted win rate on run defense, the Niners do have the talent up front to magnify any run game struggles for Los Angeles.

San Francisco's primary defensive question concerns their personnel in the secondary.

49ers' secondary problems persist

The 49ers saw their secondary depth suffer a blow right off the bat as Jason Verrett tore his ACL in Week 1, and the way in which the coaching staff have managed the personnel in the defensive backfield has received criticism.

Despite impressing early, rookie fifth-round pick Deommodore Lenoir has been conspicuous by his absence since the Week 3 loss to the Green Bay Packers, with veterans Josh Norman and Dre Kirkpatrick ahead of both Lenoir and fellow first-year corner Ambry Thomas on the depth chart.

Kirkpatrick is out on Monday with an ankle injury while Norman (ribs) is questionable, meaning both Lenoir and Thomas are likely to be in uniform, with one potentially set to start alongside Emmanuel Moseley and K'Waun Williams at corner.

Lenoir would appear to be the frontrunner to start if Norman cannot play, and the Niners may require an improvement on his generally solid play across the first three weeks for them to have a hope of containing Matthew Stafford and the Rams' passing attack.

The former Oregon corner's adjusted open percentage allowed of 35 is inferior to the average of 31.15 for cornerbacks and, beyond the threat posed by Beckham, Lenoir will also have to deal with the NFL's most productive receiver should he be thrust back into the starting line-up.

Cooper Kupp is on pace for over 1,900 receiving yards having already surpassed 1,000 through nine games. He is recording a burn, which is when a receiver wins his matchup with a defender on a play where he is targeted, 66.7 per cent of the time, with his average of 4.3 burn yards per route the best in the league among receivers with at least 20 targets heading into Week 10.

San Francisco's secondary can at best be described as being in flux. If the 49ers cannot find a combination that works, it could provide Kupp with the chance to deliver another hugely productive performance and leave Kyle Shanahan's men with the difficult task of keeping pace with the Rams' offense.

Moore thrown in at the deep end

The Niners can afford to have confidence of going blow for blow with the Rams, if they can avoid the turnovers that ultimately doomed them against the Cardinals.

Shanahan's offense has been moving the ball efficiently, with Jimmy Garoppolo producing his two best performances of the season over the last two games.

Garoppolo reached the 320-yard mark in the win over the Chicago Bears and the loss to the Cardinals, marking the second time in his career he has produced a streak of successive 320-yard games. The only other 49ers quarterbacks with multiple streaks of consecutive 320-yard games are Joe Montana (four) and Steve Young (two). 

His hopes of stretching that run to a third game may well hinge on the play of a rookie offensive lineman.

The Niners will be without right tackle Mike McGlinchey for the rest of the season after he tore his quad against Arizona. His replacement is expected to be rookie Jaylon Moore, who delivered an admirable showing in relief of left tackle Trent Williams versus the Indianapolis Colts in Week 7.

Moore is credited with winning nine of the 12 one-on-one pass protection matchups he has faced so far but, having spent his entire career to this point on the left side, looks set to flip to the right in extremely trying circumstances.

Three-time Defensive Player of the Year Aaron Donald's versatility should see him regularly shift from the interior and line up across from Moore on the edge, and the Rams will surely look to get Miller one on one with the rookie consistently.

Donald has won a remarkable 59 of his 91 one-on-one matchups and Miller's win rate of 43.94 per cent is still way above the average for edge rushers of 21.88.

The challenge for San Francisco will be to get Moore as much help as possible from tight ends and running backs to prevent that duo padding those numbers.

Leave him to fend for himself, and the Niners' hopes of keeping pace with Los Angeles could vanish in a hurry. After being embarrassed by a division rival last week, setting Moore, and in turn Garoppolo, up for success is crucial to them avoiding the same fate in the primetime finale to Week 10.