MANKATO – Vikings Pro Bowler Jerome Felton likely will miss the rest of the preseason after undergoing an emergency appendectomy on Wednesday afternoon.

The veteran fullback attended the team's morning walk-through on the final full day of training camp but was absent from the afternoon practice. It turns out Felton was rushed back to the Twin Cities for surgery to remove his appendix.

The Vikings confirmed the surgery, which was first reported by the Star Tribune via Twitter, and shortly afterward Felton (@jfelton45) tweeted: Thanks for the well wishes everybody, I'll b fine, surgery went great and I'll b out there soon! #SkolVikings

The timeline for Felton's recovery should be approximately two weeks. But it's almost certain the team will keep Felton out of game action until the regular season opens Sept. 8 in Detroit.

The Vikings will play their second preseason game Friday night at Buffalo and follow nine days later with an NBC-televised "Football Night in America" contest at San Francisco. The preseason finale will be Aug. 29 at Mall of America Field against Tennessee. But significant starters, even if fully healthy, aren't expected to play in that contest.

Felton enjoyed a major breakthrough in his first season with the Vikings in 2012, using his toughness and tenacity as Adrian Peterson's lead blocker to earn a Pro Bowl invitation. Peterson rushed for 2,097 yards on his way to MVP honors and has said that Felton's efforts blocking in front of him may have been "worth 600-700 yards over the course of the season. Maybe more than that."

Competition heats up

The Vikings finished their three-week stint at Minnesota State Mankato on Wednesday, and coach Leslie Frazier said it's too early to determine exactly how many spots will be open at each position on the team's 53-man roster.

That list must be finalized Aug. 31, but with so many moving parts in play, special teams roles, practice squad candidates and preseason game performances all will be taken into account.

The Vikings have obvious depth on the defensive line and at safety. And the team's hardest roster decisions might come at receiver and linebacker.

The Vikings' top four receivers are Greg Jennings, Jerome Simpson, Cordarrelle Patterson and Jarius Wright. But it's still not certain whether the team will keep one or two more with Joe Webb and Stephen Burton in the mix, plus Chris Summers and Adam Thielen showing promise.

"It's too early right now to order them," Frazier said. "I want us to be able to get a few more game situations under our belt."

At linebacker, Erin Henderson and Chad Greenway are locked in as starters. That leaves Marvin Mitchell and Desmond Bishop competing for the weakside spot. In addition, the Vikings have two draft picks — fourth-rounder Gerald Hodges and seventh-rounder Michael Mauti — they are rallying behind, plus continued admiration for Audie Cole's development. On top of that, Larry Dean and Tyrone McKenzie are established standout special teams contributors. So even if the Vikings go heavier at the position and keep seven instead of six, the decisions will be tough.

"Our backup linebackers are generally some of our core special teams players," Frazier said. "So not only do you have to be good on defense as a backup. But we need you to be a solid special teams player for us."

Four times two is …?

Vikings starters will see a lot of first-half action in the next two preseason games. That's good news for quarterback Christian Ponder, who played only one series and threw only two passes — one a completion and one an interception — in Friday's loss to Houston at Mall of America Field.

"Hopefully I can more than quadruple that number," he joked. "And hopefully play a lot more … I guess the plan is at least a quarter.

"… These next two games are crucial for us as an offense — we're going to get a lot of snaps," Ponder added.

Heading north

The 15 days of practice in Mankato were marked by good weather and basically good health for the Vikings.

"It was a good three weeks," Simpson said. "I loved the enthusiasm of all the guys … Everyone was striving to get better."

Said tight end Kyle Rudolph: "They had a very tough training camp for us. Coach Frazier likes to set the standard very high, and I think everyone on our team responded to that very well."

Etc.

• How much do starters need to play during the preseason to get sharp for the regular season? There might not be a good answer to that question.

"I'm not too experienced with that," second-year safety Harrison Smith said. "Last year, I just played whenever they wanted me to. It'll be the same this year. I guess you just have to try to get better any time you are on the field, whether it's practice or a game."

• After missing the Texans game because of a hamstring injury, rookie cornerback Xavier Rhodes will get a long look against Buffalo. "We want him to get a feel for the speed of an NFL game," Frazier said.

Josh Robinson and Chris Cook will be the starting corners, with Rhodes getting a lot of action as the outside corner in nickel packages.