ORCHARD PARK, N.Y. - With LeSean McCoy's playing status uncertain because of a hamstring injury, Bills coach Rex Ryan is no longer second-guessing his decision to have Karlos Williams stick to playing running back.

Announcing there's a "real possibility" that McCoy won't play against the New York Giants on Sunday, Ryan revealed he briefly toyed with the idea of having Williams switch back to his more natural position of safety.

"It was tempting," Ryan said Wednesday, recalling how impressed he was watching tape of Williams play defence during his first two seasons at Florida State. "But I'm kind of glad we left him at running back."

What a mistake that would have been.

The rookie fifth-round draft pick leads Buffalo with 186 yards rushing. And he has become the NFL's ninth rookie to score in his first three games since 1960 — and first since Robert Edwards scored in his first six games for New England in 1998.

As a result, the Bills running attack hasn't lost a step with McCoy slowed by a strained left hamstring that's nagged him since he was initially hurt on Aug. 18.

Ryan hasn't ruled out McCoy from playing, but acknowledged it "doesn't look good."

He said the team is weighing the option of having McCoy sit out to give the injury time to heal.

Though McCoy has played the past three weeks, he has not been the dynamic playmaker the Bills were relying upon acquiring him in an off-season trade with Philadelphia. McCoy has been limited to 43 carries for 146 yards, and also has seven catches for 83 yards and a touchdown.

That's a considerable drop off for a player who led the NFL with 1,607 yards rushing and 2,146 yards from scrimmage just two years ago.

Following a 41-14 win at Miami last weekend, McCoy complained the injury was acting up and added he "can't really go like I want to."

The Bills (2-1) might be down another offensive starter after receiver Sammy Watkins hurt his right calf at Miami.

Watkins was held out of practice Wednesday and isn't sure if he'll be able to take the field on Thursday. Though he wants to play, Watkins noted he doesn't want to rush back too early after spending much of last season playing through a series of injuries.

Buffalo has plenty of depth at receiver with Percy Harvin, Robert Woods and Chris Hogan, who scored on a 38-yard touchdown catch against Miami. Also, speedster Marquise Goodwin is set to return after missing the first three games with a rib injury.

The Bills lack depth at running back with Williams and Boobie Dixon as McCoy's only two backups. Receiver and return specialist Marcus Thigpen could shift to running back. Another option is promoting Cierre Wood off the practice squad.

Williams' workload has steadily increased.

After being limited to six carries in each of his first two games, he had 12 carries for 110 yards against Miami to become Buffalo's first player to top 100 yards rushing since C.J. Spiller had 105 in Buffalo's 2013 season finale.

At 6-foot-1 and 230 pounds, Williams has a powerful, straight-ahead running style, and has been effective in finding holes and following blockers.

Guard Richie Incognito was surprised to learn Williams made the switch to running back during his junior year at Florida State.

"For his vision and his feel for it, he's a natural fit for running back," Incognito said. "You'd think he'd have been playing his whole career."

Williams was a backup safety before getting his break at running back two games into the 2013 season after starter James Wilder hurt his shoulder.

The Bills were the only NFL team to express much interest in Williams before the draft. He interviewed with team officials at the scouting combine in Indianapolis, and his only pre-draft visit was to Buffalo.

"Very proud to be able to represent the team that showed me the most love," Williams said. "I'm happy about the success, but it doesn't stop there."

NOTES: Starting RG John Miller did not practice because of a groin injury. ... S Aaron Williams returned to practice for the first time since hurting his neck in a 40-32 loss to New England on Sept. 20.

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