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After three seasons spent almost entirely on San Francisco's practice squad, Dominique Zeigler is making his mark for the 49ers.

The undrafted free agent receiver has turned heads in training camp and may have earned a spot on the active roster as the fourth receiver.

"Dominique's a unique guy," coach Mike Singletary said. "He doesn't mind going across the middle, going underneath, doing some of the dirty work. He's a guy that does everything for us and wears a lot of different hats. He can play any of the receiver positions, gives us some flexibility. And he's really good on special teams as well."

Zeigler's versatility became more important to the 49ers this week after the team released veteran receiver Brandon Jones, San Francisco's top pickup in 2009 free agency.

The 49ers gave Jones a five-year, $16 million deal last year, but he became expendable by the emergence this summer of Zeigler, who wasn't drafted in 2007 out of Baylor.

Zeigler made San Francisco's practice squad that season and since then has seen numerous receivers come and go on the roster while he patiently waited for his opportunity.

With starter Michael Crabtree sidelined with a neck sprain, Zeigler took snaps with San Francisco's first-unit offense during team drills Wednesday. Zeigler appears to have climbed past veteran Jason Hill as the 49ers' No. 4 receiver behind Crabtree, Josh Morgan and Ted Ginn.

"I knew my time would come as long as I keep working hard," Zeigler said. "And when my time comes, I just have to take grab of it with both hands."

Zeigler worked his way onto the 53-man roster in 2008, then onto the field over the last half of that season when he had five catches for 97 yards and contributed seven tackles on special teams.

Zeigler was in competition to make the final roster last summer before he sustained a high ankle sprain in San Francisco's final exhibition game. He spent the entire 2009 season on the 49ers' practice squad.

This summer, Zeigler has been one of the 49ers' more impressive and consistent performers. He had one catch for 18 yards and returned one punt 11 yards in San Francisco's 37-17 preseason opener at Indianapolis last week.

"Dominique has had an outstanding camp," offensive coordinator Jimmy Raye said. "But a year ago I saw the same things. It just didn't come to fruition because he was injured in the last exhibition game. This time, he's stayed, he's been healthy and he's taken another step. Right now, it's what you've seen in a pretty good performance."

Zeigler, who carries 185 pounds on his slender 6-foot-3 frame, gives the 49ers a tall target that can play all three wide receiver positions. As he beat defenders for several catches Thursday, Zeigler continued to look like a natural.

"We've moved him around a bunch in there and every time he goes in he knows what he's doing," Smith said. "All the quarterbacks feel good about throwing him the ball in traffic because he is so strong-handed. He's a guy that everyone in the huddle feels good about when he steps in. He just continues to do it."

EXTRA POINTS: LB Travis LaBoy returned to full practice for the first time since sustaining a concussion during the first week of training camp. ... Newcomer RB Brian Westbrook was given the morning practice off, his second consecutive veteran courtesy. ... OL Tony Wragge continues to get more time at both guard positions with veteran Adam Snyder out due to a concussion. ... S Reggie Smith came down with a leaping interception during team drills and continues to impress this summer. The third-year veteran returned an interception 91 yards for a touchdown last week against the Colts. ... Sunday's game will be the first time the Vikings have ever played a preseason game in San Francisco. Singletary will wear a wireless microphone for the "Sunday Night Football" broadcast on NBC.