Ray McDonald said staying fresh will be a challenge against New England's high-tempo offense. (US Presswire)

Several 49ers tuned into Monday Night Football to get a glimpse of their next opponent, the New England Patriots. By the end of the first half, they'd seen enough.

The Patriots built a 21-0 halftime lead and were well on their way to their way to their 20th straight home victory in the month of December, and doing it against Houston, which came in with the NFL's best record.

"I didn't look too much once the score got up to 21-zip," DE Ricky Jean Francois said. "It's like playing PS3, put the sticks down."

The 49ers will try to become the first team to win in Foxboro in December since the Chad Pennington-led Jets did it in 2002.

San Francisco has seen some good quarterbacks this year -- Aaron Rodgers, Drew Brees, Eli Manning, even Russell Wilson -- but Tom Brady will present unique challenges Sunday. Brady, the league's top-rated passer, has thrown for 3,833 yards with 29 touchdowns and four interceptions. 

For DE Ray McDonald, it's the Patriots' tempo that stands out.

"I think they say they run a play every 25 seconds and that's tops in the NFL" he said. "We haven't faced an offense like that yet. It doesn't give you a chance to substitute on defense, on the defensive side of the ball. We got to hang in there, we got to gut it out."

McDonald wasn't watching at the end of the game to see if Houston had tired defensively, but said staying fresh will be a challenge.

"That's where preparation comes in," he said. "You got to come out in practice this week … and I'm pretty sure the coaches are going to do a good job of having the scout team give us an up-tempo type practice, and they're going to get us ready for this game on Sunday."

Although New England's passing game gets its share of attention, its rushing game has also proved effective. The Patriots rank No. 7 in the league in rushing (139.9 ypg), just 21.6 yards a game fewer than San Francisco's No. 2-ranked unit. RB Stevan Ridley is seventh in the league with 1,082 yards rushing.

"(Their offensive line is) a physical bunch," McDonald said. "They work together, they're smart. Just watching them last night, they're not a finesse team."

The Patriots opened as three-point favorites, but the line has since moved to New England minus-5.5. It's a rare position for the 49ers, who had been favored in every game except their season-opening trip to Green Bay this season by oddsmakers.

"We enjoy being the underdog," CB Tarell Brown said. "Any time you play football, you always have a chip on your shoulder, you always have something to prove every week. This week we have to go out there and win a big game."

Jacobs suspension not surprise: The suspension of Brandon Jacobs for the rest of the regular season wasn't a big surprise to players on the team.

"From the coaching standpoint, they don't want any distractions on the team. He was being a distraction, they felt he was being a distraction, so they felt they needed to do something about it," McDonald said.

When asked if he agreed with the suspension, McDonald replied: "I guess. If he’s not about the team. And the coaches feel that he’s not trying to help the team, they made the right decision.”

Dobbs on Injured Reseve: The 49ers announced Tuesday they have placed DL/TE Demarcus Dobbs on IR. He was carted off the field after a knee injury against Miami on Sunday and was on crutches after the game.

With the injury to Dobbs and the suspension of Jacobs, there are two open spots on the 53-man roster.

Primetime performers: Sunday's game against the Patriots is the 49ers' fifth primetime game this season. They're 4-0 and have outscored opponents 96-35.

"We thrive on games like this," McDonald said. "When you're a little kid, you want to play in games like this. That's what we all talk about throughout the season. These primetime games, these are games that when you're growing up you're like, 'Man, I wish I could be in a game like that.' Once we're here and we're playing in those games, guys perform at their highest level."

The NFL also announced Monday that San Francisco's game next week at Seattle has been flexed for primetime.

McCoy doesn't pass physical: The 49ers were reportedly close to signing eight-year veteran LB Matt McCoy, but he didn't pass his physical according to the Sacramento Bee's Matt Barrows. 

Follow 49ers reporter Kyle Bonagura on Twitter @CBS49ers and @KyleBonagura.