Rookie quarterback Robert Griffin III is practicing after suffering a concussion last week, and it looks like he'll get a crack at snapping the Washington Redskins' eight-game home losing streak.

The Minnesota Vikings will have running back Adrian Peterson in their bid for a fourth straight victory in the nation's capital as he appears fully recovered from a season-ending knee injury suffered there in 2011.

Peterson and the surprising Vikings go for a fourth straight victory overall and sole possession of the NFC North lead Sunday.

Concerned that Griffin -- the league's leading rushing quarterback with 241 yards -- was more susceptible to injury, the Redskins (2-3) did not call a running play for the 2011 Heisman Trophy winner in last Sunday's 24-17 loss to Atlanta. Griffin, though, was knocked out in the third quarter when linebacker Sean Weatherspoon leveled him on a scramble after he failed to find an open receiver on a third-and-goal play.

Griffin attended a Rookie Success Program meeting Monday morning and completed the NFL's concussion protocol before he was allowed to practice Wednesday.

Griffin was a limited participant in practice Thursday but took part in a full practice for the first time this week Friday, leaving coach Mike Shanahan confident Griffin will start Sunday.

"If he passes his tests and we don't see any symptoms, then it looks like he'll be ready to go," Shanahan said.

The Vikings (4-1) arrive with plenty of confidence as they're off to their best start since opening 6-0 en route to a division title in 2009. With a win at Washington, Minnesota will move one-half game in front of idle Chicago.

"I know everyone else is surprised that we're 4-1. What stinks is that we should be 5-0," said quarterback Christian Ponder, referring to a 23-20 loss at Indianapolis on Sept. 16.

Ponder's development in his second year has given the Vikings a legitimate passing threat -- he has a 95.5 passer rating and his 69.0 completion percentage is second only to Griffin (69.1). But a bigger reason Minnesota is riding its best stretch since winning four straight Nov. 1-29, 2009, might be Peterson's quick return.

The four-time Pro Bowl back suffered a torn ACL and MCL on the Vikings' first offensive play of the second half of a 33-26 win at Washington on Dec. 24. Ponder suffered a head injury on the next play on a sack, and he left the game for good after taking one more snap.

Peterson didn't play this preseason as he rehabbed from those injuries, but he has 420 yards and two scores thus far. Peterson has also answered questions about his breakaway speed as he's tied for second in the NFL with four rushes of 20-plus yards.

The Vikings, ninth in the league with 666 rushing yards, expect Peterson to be available Sunday after he suffered a mild left ankle sprain in last Sunday's 30-7 victory over Tennessee.

"When it's the same leg where you had the knee injury, I can see there being a little bit of doubt in your mind about what is going to happen next but to his credit once again, he kept himself together, got back on the field. He ran great," coach Leslie Frazier said of Peterson, who finished with 88 yards on 17 carries.

So has Percy Harvin, who has become the team's go-to receiver on bubble screen passes that maximize his versatility. He is tied for second in the NFL with 38 catches, and 329 of his 407 receiving yards have come after the catch.

"A beast, that's probably a good way to describe him," Ponder said after Harvin had a rushing and receiving score last week. "We're going to keep giving him the ball."

The Redskins will continue to rely on rookie Alfred Morris, who had a season-high 115 rushing yards last week and has 491 overall. Morris, a sixth-round pick, and Griffin are tied for the team lead with four rushing TDs, with Griffin's total having already tied the single-season team record for a quarterback.

Washington, though, will face an improving Vikings defense that's allowed one rushing TD. Minnesota held former 2,000-yard rusher Chris Johnson to 24 on 15 carries last Sunday and the Titans to 52 overall on the ground.

"It's exciting to know that every week you have a chance. It's exciting to know that with so many questions going into this year, it's exciting to answer 'OK, if we play our best, we have a chance to beat anybody in the NFL,'" end Jared Allen said. "And we're pretty darn good if we play our best."

The Redskins' last home win was 22-21 over Arizona on Sept. 18, 2011.