The San Diego Chargers and Minnesota Vikings have been forced to adapt as their running back situations have significantly changed. Chargers running back Ryan Mathews might be out longer than expected and Vikings running back Adrian Peterson is unlikely to return this season.

The Chargers have much deeper issues at the position. Mathews went down in Week 2 due to a sprained MCL and Danny Woodhead broke his leg in Week 3. Donald Brown, the next running back in line, has failed to produce with 126 yards on 59 touches. After Brown suffered a concussion against the Jets in Week 5, third-string Branden Oliver stepped up and has proved effective. The undrafted rookie has rushed for 249 yards on 57 carries (4.4 average) with two touchdowns to go along with 12 receptions for 124 yards and a touchdown in four games this season.

But San Diego will need Mathews back to provide stability at the running back position and some experience as well. Mathews has been a starter and played with quarterback Philip Rivers ever since he was drafted before the 2010 season. Unfortunately for the Chargers, and according to the San Diego Union Tribune, Mathews has not yet been cleared to run and will likely miss the next two weeks of action. The Chargers' bye is not until Week 10, and based on the way Oliver has been performing, the team may opt to keep him out until then as a precaution.

"I'm just taking it one day at a time," said Mathews, in thus UT San Diego article. "When they think it's time for me to start running, then it's time to start running. It's all in their hands." The Chargers are 5-1 and will face the Chiefs, Broncos and Dolphins before their bye week.

In Minnesota, the Vikings are likely without Adrian Peterson for the remainder of the year because of his indictment on child abuse charges. The team has turned to backup Matt Asiata to carry the load, but after Weeks 2 and 3, he carried the ball 25 times for only 71 yards and no touchdowns. Minnesota has begun working running back Jerick McKinnon into the mix ever since he impressed in Week 4 with 18 carries for 135 yards. Asiata received 20 carries that game, but gained only 78 yards despite scoring three touchdowns.

Over the past two games it seems as if the two are splitting carries, with Asiata totaling 17 touches for 68 yards and McKinnon adding 18 for 64 yards. But this week Minnesota will face the Bills who boast a staunch run defense, and they may turn to Asiata, who is more of a power runner, to establish the running game. According to Bills reporter Joe Buscaglia, Vikings head coach Mike Zimmer told reporters on a conference call that he would like for Asiata to get more carries than McKinnon this week.

But Asiata has been dealing with a groin issue and has averaged only 3.5 yards per carry this season compared to McKinnion's 5.0 ypc. McKinnon also has 23 fewer rushes and is only 20 yards behind Asiata, so it's sort of a mystery as to why Zimmer would want to use Asiata more against a Bills' defense that has allowed only 67.5 yards per game on the ground and just 2.8 yards per carry. McKinnon is also the superior athlete, which would serve them better because the only running back the Bills have shown weakness against this year were Chicago's Matt Forte in Week 1 (17 carries for 82 yards), who is an all-around athletic and versatile player.

So fantasy owners might want to beware of Asiata and McKinnon for Week 7 and only start them if your roster is seriously lacking in the running back department.