Our snapshot look at the Vikings as they prepare for Sunday's game against the Steelers in London:

Player in the spotlight

Harrison Smith, Vikings

The second-year safety got beat on Cleveland's game-winning touchdown last week, but he has been one of the defense's best playmakers. In three games, he has produced 26 tackles, two interceptions, three pass breakups and a forced fumble.

Smith faces another challenge this week against a Steelers team that ranks 10th in the NFL in passing offense. The Vikings have a depleted secondary, which puts even more pressure on Smith to be a steady presence.

Despite their health issues, Smith said he can't overcompensate in trying to help backups who are pressed into action.

"You might think that [way] from the outside looking in, but you really can't do that because then you're going to compromise your job," Smith said. "You've just got to trust the guys around you. We've got young guys, but they're coming along and doing their job."

Keep an eye on

Everson Griffen. NFL pundits — including Peter King — predicted a breakthrough season for the backup defensive end after he collected five sacks, one interception and 16 quarterback hurries in the Vikings' final seven games last season.

So far, Griffen's impact has been fairly limited. He has accounted for only six tackles, one quarterback hurry and one pass breakup while playing 61 percent of the defensive snaps.

"He's trying as hard as he can," coach Leslie Frazier said. "He just hasn't been able to get those splash plays that we saw at the end of last season. He's getting close. It just hasn't quite clicked yet."

Griffen gives the Vikings another pass rushing threat, especially in nickel situations when he slides over to tackle. He said he's not discouraged by his lack of productivity.

"It's going to come. I'm not worried about it," he said. "I think I'm playing some good ball. I can play a lot better than what I am. But it's eventually going to come like I want it to."

Most pressing question

The Steelers have been pretty one-dimensional in the first three games, relying primarily on their passing game. They could stick to that same script against the Vikings' 28th-ranked pass defense. Of particular concern for the Vikings is quarterback Ben Roethlisberger's ability to keep plays alive with his feet.

Roethlisberger uses his strength to avoid sacks and buy time for his receivers to get open. That puts pressure on defensive backs because it forces them to stay in coverage longer.

"He's not a guy who is going to break out of the pocket and run," defensive end Jared Allen said. "But he's a guy who is really shifty in the pocket and very hard to get on the ground and then he makes the big play downfield. When you get to get a hand on him, you got to get him down. You might have to cover six, seven, eight seconds on a play. That's kind of where he presents himself."

Steelers scoops

Rookie running back Le'Veon Bell is expected to make his NFL debut after missing the first three games because of a foot sprain, according to published reports. Bell's return could help jump-start the Steelers running game, which ranks 30th at only 51.7 yards per game.

"Interested in seeing what he can bring to the table because we've never really seen him in a game situation," Roethlisberger said.

Injury report

The Vikings secondary will be extremely thin after starting cornerback Chris Cook (groin) and starting safety Jamarca Sanford (hamstring) were declared out on Friday. Tight end Rhett Ellison (knee) also is out. At cornerback, that leaves the Vikings with Josh Robinson, rookie Xavier Rhodes, A.J. Jefferson and Marcus Sherels. Jefferson was bothered by an ankle injury in practice this week.