The danger of ranking running backs in August was made perfectly clear last Thursday, when we learned Browns rookie Trent Richardson would have knee surgery.

Later that night, the Chargers' Ryan Mathews fractured his clavicle in San Diego's preseason opener and is expected to miss 4 to 6 weeks.

You could say we've made some changes to these rankings.

Some notable updates from the running back rankings we posted Aug. 8 (the above link reflects our current rankings):

-- Chargers coach Norv Turner said Mathews' injury is "not so bad." I can only hope. In a keeper league in which I participate, I traded for Mathews prior to training camp and now must decide if he will still be one of my three keepers (probably).

The Chargers open the season Monday, Sept. 10 at Oakland --  31 days after Mathews' surgery. The guess here is Mathews will return in Week 2 against Tennessee, and considering the lack of studs at the position, I think he remains a top-10 player at the position.

Yes, injuries are a concern -- Mathews has played 26 games in two years. But consider this: Last season, he averaged 4.9 yards per carry and caught 50 passes. In 14 games, he racked up 1,546 total yards.

Would you rather have Mathews coming off a shoulder injury or Adrian Peterson following an ACL tear.

I'll take Mathews.

-- Richardson, who is expected to start the Browns' opener against the Eagles, dropped from No. 14 to 17.

-- The (expected) uncertainty of the backfield situation in Washington -- Mike Shanahan, tormenting fantasy owners since 1995 -- has resulted in Roy Helu dropping from No. 24 to 29 at running back. Redskins teammate Evan Royster, who could be Washington's featured back (your guess is as good as mine when it comes to Shanahan), went from unranked in the top 50 to No. 41. Another Redskin, the (always) beat-up Tim Hightower, dropped from No. 41 to out of the rankings.

-- Ronnie Brown, who would start the season opener for the Chargers if Mathews can't go, is in the top 50 at No. 47. Don't get too excited about Brown, who averaged 3.2 yards per carry in a limited role for the Eagles last season.