San Francisco 49ers head coach Kyle Shanahan thinks he has a roster built for the long haul.

That's an advantage over most other teams, Shanahan said when he spoke to the media after roster cut-down day.

"This is the third year in a row that I feel we have a chance in every game we're in," Shanahan said. "That's all you can ask for from a talent standpoint. I don't feel like everyone, year in and year out, always does have a chance.

"To be there three years in a row … I feel real good about it."

The 49ers are in a good spot as they begin the 2021 NFL season against the Detroit Lions at Ford Field Sunday. They have talent on both sides of the ball, and Shanahan has one of the keenest offensive minds in the league.

But the specter of injuries, and how they can reduce a roster to rubble – as happened to the 49ers last year – is ever present.

And hanging over the 49ers is the question of when, not if, rookie Trey Lance will take over at quarterback for injury-prone veteran Jimmy Garoppolo.

Here is a look at the 49ers – 2020 injuries, offense, defense and their QB question:

Injuries: Without them, the 49ers might not have dropped from a 13-3 won-loss record and a trip to the Super Bowl in 2019 to 6-10 and out of the playoff race early in 2020. They certainly didn't help.

The carnage started in the opener and continued throughout the season.

Among the key injuries:

Defense: Outside linebacker Dee Ford went out for the season in the opener with neck and back injuries. Defensive ends Nick Bosa and Solomon Thomas (signed with the Raiders in 2021) went out for the season in Game 2 with knee injuries. Cornerback Richard Sherman played only five games.

Offense: Garoppolo played only six games. He had seven TD passes, five interceptions and a 3-3 won-loss record. Make of him what you will, the 49ers were 3-7 without him.

Two-time Pro Bowl tight end George Kittle and running back Raheem Mostert missed eight games. Wide receiver Deebo Samuel missed nine.

Bottom line: The cumulative effect of injuries is reflected in the won-loss record. The 49ers were 4-4 at the halfway point, with a chance to make the playoffs as a wild card (the Bears made it at 8-8).

They skidded to a 2-6 record in the second half to finish 6-10 and last in the NFC West.

Offense: The Lions know what to expect from the 49ers. Stopping it is another matter.

"There are few that do a better job than Shanahan, and he's got weapons," said head coach Dan Campbell. "It starts with Kittle. The things they are able to do … mix up the run game, play pass, and a lot of eye candy to try to get you on your heels.

"This is a huge test for us. It's a good team, and it's a well-coached team."

Outside linebacker Romeo Okwara, the Lions' leader with 10 sacks last year, said it's important not to get tricked by the 49ers with their formations and motion.

"They do a lot of window dressing," Okwara said. "The biggest thing is training our eyes. Film study is going to be huge all week."

Defense: The impact of injuries is evident in comparing a relatively healthy roster in 2019 to the 2020 unit.

In 2019 the 49ers had 48 sacks, 87 tackles for loss and 93 quarterback hits. They dropped to 30 sacks, 67 tackles for loss and 72 QB hits in 2020.

"DeMeco Ryans (the new defensive coordinator) is putting his own kind of spin or flavor on this defense," Campbell said. "It's an attacking style defense. They've got certainly some pieces up front.

"They have a damn good middle linebacker (Fred Warner), and a pretty good secondary."

This makes for a good first test of 2021 for the Lions' offensive line to protect QB Jared Goff and open lanes for the running backs.

49ers QB question: There is no assurance one way or another if Lance will get some playing time. A chipped bone in his passing (right) hand in the preseason could delay his debut.

When asked if he expects Lance to play, Okwara replied:

"I have no clue, but we're going to be prepped if he gets out there. I think everyone knows he can use his legs."