Vikings coaches talk about fourth-round draft pick Christian Ballard the way a lottery winner would if he had found his ticket at the bottom of a trash bin.

"We thought we were really getting a coup in where we took him in the draft. He has not disappointed," coach Leslie Frazier said.

The rookie defensive tackle from Iowa, a projected second-round pick in April, fell to the fourth round amid reports he failed a drug test at the NFL combine.

So far, the Vikings can thank their peers for passing on the versatile, 6-4, 283-pounder who seems to be learning quickly.

Frazier said he's comfortable enough to play Ballard -- who has two sacks in three exhibition games -- at defensive end for the first time in the team's preseason finale Thursday against Houston. It's another sign that his stock within the franchise continues to rise.

"Sometimes, yeah, I surprise myself in how I can keep up with the speed a little bit," Ballard said. "But I have high expectations for myself."

As the draft neared in April, reported that Ballard tested positive for marijuana at February's NFL combine. Ballard's "mistake" -- he hasn't officially confirmed the report -- scared NFL executives who passed on the Kansas native until the Vikings grabbed him on the final day of the draft.

Last year, Ballard finished with 43 tackles and three sacks as a member of Iowa's talented defensive front. The report, however, seemed to nullify lofty projections about his NFL future.

Ballard said the setback never threatened his outlook on his pro career, although he said proving doubters wrong "is always fun."

"It's just a short little hiccup in my career. It's nothing that I can control now," he said. "The only thing I can do is look forward to the future. I'm in a great program in Minnesota. I love the coaches here. I love the atmosphere. The team's great. ... I don't really have any regrets."

In the Vikings' 23-17 loss to Dallas on Saturday, Ballard crashed into the Cowboys offensive line late in the second quarter and tracked down Tony Romo for his second preseason sack.

He's the No. 3 defensive tackle behind Kevin Williams, who is injured and might be facing a suspension in the StarCaps case, and Letroy Guion. Against the Cowboys, however, the Vikings used Ballard as the nose tackle in their No. 1 nickel package. The team employed the nickel on half of its defensive sets in 2010, so the move suggests Ballard could see a lot of snaps during the regular season.

The Vikings wouldn't thrust Ballard into so many schemes if it didn't trust him, defensive line coach Karl Dunbar said.

"He's a smart kid so we try to put him in the game in all sorts of situations," Dunbar said. "The more he can take, the more we'll give him."

The multitude of roles puts continuous pressure on Ballard to remain flexible and absorb the playbook, a more challenging position for this season's rookies because of time missed during the lockout. But a seasoned core of veterans on the defensive line offered to help.

"I think he does one good thing that I think all rookies should do: he's been picking Kevin Williams' brain," defensive end Jared Allen said. "He's progressively getting better. ... He's got a lot of work left. We try to tell him it's going to crank up a notch or two. The sacks don't come as easy as they've been coming for him."

All of the praise, extra positions and elevated expectations suggest that Ballard has played his way into one of the team's coveted roster slots, with final cuts set for Saturday.

But he discussed the significance of Thursday's game as if the first three preseason games hadn't happened.

"For you to stay in this business, you've got to produce. And you've got to be an attribute to the team," he said. "As a rookie with the last preseason game coming here, you definitely got to be focused."