Start or sit: Should fantasy managers play Brock Purdy, Matthew Stafford and Nick Chubb today?

Week 13 in the NFL is already at full steam. It began on Thanksgiving, with a trio of games between the Chicago Bears and Detroit Lions, New York Giants and Dallas Cowboys and Miami Dolphins and Green Bay Packers. Then came Black Friday, a new tradition around the league, and yet another dramatic escape by the Kansas City Chiefs against the Las Vegas Raiders.

But there's still a whole Sunday left to play, with an enticing slate of games on tap. And that means there's still need for fantasy advice, so we've got you covered: Here are three start/sit recommendations on key players who could make or break your lineups this week.

Sit: QB Brock Purdy, San Francisco 49ers

Purdy has been able to gradually ramp up his throwing program this week without a setback to his injured shoulder, and it now sounds like he's set to play in the San Francisco 49ers' big showdown with the Buffalo Bills on Sunday. But while this is a big boost to the Niners' chances, don't be fooled into firing up Purdy in your fantasy lineups.

Sure, the Bills have allowed some healthy games to opposing QBs of late (seven passing TDs allowed over the last three games), and Purdy's mobility has given his fantasy value a boost even amid a diminished San Francisco passing attack. But Buffalo has been one of the best fantasy defenses against quarterbacks all year long, and they're well-rested after a bye in Week 12. Combine that with the awful weather expected in Buffalo on Sunday night, the iffiness around Purdy's health and the fact that he likely won't have star tackle Trent Williams in the lineup, and this seems like a disaster in the making.

Start: QB Matthew Stafford, Los Angeles Rams

Stafford, on the other hand, is in a smash spot on Sunday. The veteran has been a totally different quarterback with Puka Nacua and Cooper Kupp in the lineup, averaging 281.6 passing yards and 2.4 touchdowns per game since getting both of his top options back in Week 8. He even delivered against a stingy Philadelphia Eagles secondary last week, with a late touchdown salvaging his night.

Now he gets a New Orleans Saints secondary that got torched by Jameis Winston the last time it took the field. Sure, the Saints are coming off a bye in Week 12, but rest and preparation can only do so much. This is a diminished unit, and far less talented passing attacks than Los Angeles' have had success against New Orleans in recent weeks. In a high-scoring affair, expect Stafford to deliver another big stat line.

Sit: RB Nick Chubb, Cleveland Browns

Chubb had his best fantasy performance in weeks in the upset win over the Pittsburgh Steelers, but that was almost entirely on the back of two short touchdowns. He finished with fewer than three yards per carry, plus only one reception for one yard.

It's entirely possible that he finds the end zone again this week, and his volume consistency gives him a relatively high floor. But the Denver Broncos are one of the fiercest defenses in the league, and have allowed just two rushing touchdowns since Week 6. Combine that with uncertainty for Cleveland on the offensive line, and it sure seems like Chubb is in for a tough night on Monday. The volume and talent are nothing to sneeze at, but he's much more a flex play than an RB2 in this spot.