Two positions that are very important are left tackle, which requires a good athlete who has the ability to protect the quarterback, and running back, which every team needs so they can run the ball effectively and help take the pressure off the passing game.

Unfortunately, the Vikings have lost their standout running back, Adrian Peterson, who has undergone surgery and might be finished as an elite NFL runner. If he does come back, he has to prove that he can come close to leading the NFL in rushing like he did last year.

The Vikings thought enough of Matt Kalil that they made him one of the highest-paid offensive linemen in the league this year at $11 million, and now he is through for the season and like Peterson might never be the same or be forced to retire because of injuries.

What's equally unfortunate is the Vikings will not be in a good position to add an elite running back or tackle in next year's draft because they traded their 2017 No. 1 draft choice and at minimum a 2018 fourth-rounder to the Eagles in the Sam Bradford deal.

However. if you want to be positive, this is what you have to think: Vikings General Manager Rick Spielman has proved to be such a genius when it comes to making trades, drafting and signing free agents that you can't sell him short on coming up with some kind of a miracle to replace two of the best players on the roster in Peterson and Kalil.

But Peterson wouldn't have been offered a contract next year even if he hadn't gotten hurt because he would have to be paid a $6 million roster bonus for reporting in the spring and an $18 million option on a contract. Spielman wasn't going to exercise that option even if Peterson duplicated last year's success because running backs aren't paid that much in the NFL anymore. And it's unlikely Peterson would have accepted a large pay cut if the Vikings let him go and offered him a smaller contract.

Free-agent issues

The Vikings do have another problem in that they could have 13 other free agents next year, not including Kalil and Peterson.

The pending free agents are running backs Zach Line and Matt Asiata, linebackers Audie Cole and Chad Greenway, tight end Rhett Ellison, offensive linemen Joe Berger, Mike Harris and Andre Smith, defensive lineman Justin Trattou, punter Jeff Locke, defensive backs Captain Munnerlyn and Terrance Newman and quarterback Shaun Hill.

There certainly are some challenges in the future facing Spielman and Executive Vice President of Football Operations Rob Brezinski, who manages the salary cap.

Other teams with the challenges listed above would fail completely.

But if you check the records of Spielman and Brezinski, and with a great coaching staff headed by Mike Zimmer, you can bet the Vikings will find a solution despite having the worst luck in losing quarterback Teddy Bridgewater, defensive tackle Sharrif Floyd, Peterson and Kalil.

Spielman pulled off the Bradford trade, and that has worked out, and the roster includes a lot of young players who have developed because of great drafts in the past.

Trainers leave U

Six trainers have left the University of Minnesota athletic department in recent months. Why they all left nobody knows. Certainly some have gotten better jobs.

The trainers are Ed Lochrie, Chris Ashton, Rich Schlotfeldt, Matt Carlson, Carly Hagler and Deb Canfield.

Lochrie is a trainer and clinical assistant at Allina's Sports & Ortho. Ashton is in the concussion program at a Twin Cities orthopedic hospital. Schlofelt is teaching in the Anoka school district. Carlson is a sports medicine supervisor at TRIA. Hagler is at Fairview Sports and Orthopedic Care. And Canfield is working in the Upstate Medical Physics residency program.

Jottings:

• Spielman and his scouts proved again they are geniuses by drafting Stefon Diggs out of Maryland, where he caught 150 passes for 2,227 yards and 14 touchdowns over his career. In his senior season he had 62 receptions but for just 792 receiving yards, a mediocre 12.8 average, and five touchdowns. Those are not exactly standout numbers. It took him four games into his rookie season to be activated, and that was partly because of injuries to more experienced players. Still, last year he led the Vikings in both receptions (52) and receiving yards (720), and this year he looks even better. He has the second-most receptions (16) and the most receiving yards (285) in the NFL this year.

• After not playing in Week 1, Vikings top draft choice Laquon Treadwell made his NFL debut Sunday, although it was only for two plays and the former Mississippi receiver did not catch a pass. Meanwhile, Washington's Josh Doctson, the former TCU receiver selected 22nd overall, one pick before Treadwell, was targeted five times in Sunday's 27-23 loss at Dallas. Doctson caught only one of those five passes, but it was for 57 yards in the fourth quarter. In Week 1, he played 12 snaps with one reception for 9 yards.

• Through three games, Notre Dame senior linebacker James Onwualu, a former Cretin-Derham Hall standout, is second on the Irish in tackles with 18, including four for loss. He had six tackles for loss all of last season.

•The Twins who got traded away in July and August haven't performed particularly well with their new teams. All-Star infielder Eduardo Nunez has seen his numbers drop off a little with San Francisco, as he has hit .273 with four homers, 19 RBI, 21 runs and 11 stolen bases in 46 games with the Giants after hitting .296 with 12 homers, 47 RBI, 49 runs and 27 stolen bases in 91 games with the Twins. Even though he was traded July 28, his 27 steals would still be tied for third in the American League as of Wednesday. … Lefthander Fernando Abad lost his first outing with Boston when he gave up a three-run homer to Seattle's Robinson Cano. He hasn't improved much since then; in 17 games with the Red Sox he was 0-2 with a 6.39 ERA. ... Ricky Nolasco was only 2-6 in nine starts with the Angels, but he had a 4.03 ERA, compared to his 4-8 record with a 5.13 ERA in 21 starts with the Twins. In that trade, the Angels acquired former Twins top prospect Alex Meyer, who earned his first major league victory by pitching five shutout innings against Toronto on Sunday. Before that, he had made two September starts and lost both, giving up five earned runs in 7⅓ innings.

Sid Hartman can be heard weekdays on 830-AM at 6:40, 7:40 and 8:40 a.m. and on Sundays at 9:30 a.m. shartman@startribune.com