Adrian Peterson has been active along the sideline at Winter Park during Vikings minicamp. The running back remains on a fast recovery from December surgery to repair torn knee ligaments.

"It's pretty much wide open. I'm able to go out and do everything -- cutting and different things like that. Flexibility is good," Peterson said.

"Main thing for me right now is really getting the strength back in this left leg, getting the quad back strong, getting the hamstring and the calf, building those muscles, trying to get it equal or stronger than the right leg."

Peterson remains optimistic his intensive rehab program will prepare him for training camp, which begins July 26 in Mankato. He wants to play in the season opener Sept. 9 against Jacksonville at the Metrodome.

"My goal is to be able to go out and participate somewhat during training camp," Peterson said. "That's my goal. How much? I'm sure the staff, they'll evaluate things and they'll let me know."

Coach Leslie Frazier still is cautious.

"We need to see him be able to cut, explode out of a cut, change direction without having any residual effects from that," Frazier said. "The next step would be to put some shoulder pads on and seeing how he takes contact and seeing how he cuts when people are coming at him."

Peterson doesn't want to judge his progress prematurely.

"It's hard to imitate actually being out there on the field and cutting on a dime," he said. "It's football, it's different."

Mystery injury

On a day when the Percy Harvin saga was dominating the news, another, smaller mystery seems to be emerging in the Vikings' linebacking corps.

Middle linebacker Jasper Brinkley was held out of practice again. On Tuesday, Brinkley said he was out because of a problem in his surgically repaired hip. On Wednesday, Frazier insisted that Brinkley was being treated for a groin injury.

They both agree that Brinkley should be ready to go by training camp. But Frazier did admit that he has a bit of concern about the position, given there is no clear-cut Plan B ready should Brinkley have further problems.

Tyrone McKenzie has been playing middle linebacker in Brinkley's absence, but he is far from experienced and the team won't really know his potential until the pads go on in training camp.

Guarded optimism

Offensive coordinator Bill Musgrave is happy with the condition of second-year player Brandon Fusco, who could be the starting right guard.

"He's really worked hard," Musgrave said. "In fact, early in the offseason he went up to Pennsylvania and worked out with some of his buddies on the Steelers, being that he's from Slippery Rock. He came back to engage in our program, and I know [strength and conditioning coach] Tom Kanavy could talk more about how much muscle mass he has gained ... but we're very excited about his future."

Etc.

• The Vikings were scheduled to practice outdoors Wednesday afternoon but moved into the Winter Park fieldhouse because of lightning strikes in the area.

• Three receivers are hampered by injury or illness. Bryan Walters left practice early because of a sprained ankle. Stephen Burton also was held from practice after being diagnosed with pneumonia. Kerry Taylor (broken finger) also missed practice.

Staff writer Kent Youngblood contributed to this report.