The Kansas City Chiefs are concerned their All-Pro running back could be out a while, and the Miami Dolphins already know their top rusher will be.

That could only amplify the problems their quarterbacks are having.

The winless Chiefs need Alex Smith to start proving he was worth that big contract, especially with Jamaal Charles' status unclear, and Ryan Tannehill hopes to begin showing he's worthy of one for a Dolphins team missing Knowshon Moreno.

This matchup Sunday in Miami features teams coming off losses which included potentially major blows to their rushing attacks.

Charles, whose 1,980 total yards last season were second in the NFL, suffered a high ankle sprain in the first quarter of a 24-17 loss at Denver last Sunday. Though Kansas City (0-2) doesn't feel the sprain is too severe and isn't listing him as out, it's the type of injury that often causes a player to miss multiple weeks -- especially a shifty one who relies on quickness.

He practiced in a limited capacity for the second straight day Friday and coach Andy Reid said he looked a little bit sore but did "OK" in the workout.

Second-year pro Knile Davis did a solid job in relief last week, gaining 82 yards and two touchdowns on 23 carries and 29 yards on seven receptions, as the Chiefs gave a scare to the defending AFC champion Broncos.

"When I go in, I know my job has been all week to pay attention to what Jamaal does," Davis said. "I've been doing good film study, watching him and what he does so if unfortunately he went down I would be able to step in and help out."

It appeared Moreno would step in as Miami's top backfield option after rushing for a Week 1-best 134 yards in a 33-20 win over New England in his Dolphins debut. Instead, Moreno will be out at least four weeks and possibly much longer after dislocating his elbow on his only carry in last Sunday's 29-10 defeat in Buffalo.

"It hurts because No. 1, he's a productive player and has proven that," Miami offensive coordinator Bill Lazor said. "No. 2, anyone who watches the game can see the emotion Knowshon plays with."

There was concern Lamar Miller, who won the starting job in the preseason with Moreno missing time following knee surgery, might also be out after leaving in an ankle boot last week. However, he's been practicing and should be ready Sunday after receiving 11 carries each of the first two games, gaining 105 yards, and that workload may significantly increase.

Miami (1-1) re-signed Daniel Thomas after releasing him last month, and the only other running backs on the roster are undrafted rookies Damien Williams and Orleans Darkva.

Neither team has displayed a reliable passing game.

Smith, less than a few weeks removed from signing a four-year extension worth $68 million, is the NFL's lowest-rated passer (63.6). He didn't throw a TD pass last week despite leading the Chiefs inside Denver's 35-yard line six times, including a fourth-down incompletion from the 2 with 18 seconds left.

Reid downplayed the notion that the pressure on Smith could grow if Charles misses significant time, the veteran signal-caller is just concerned about getting in the win column in 2014.

"It's not where you hoped to be two weeks ago," Smith said. "It's a long season though. ... The mentality is let's win this week, put some things together and you never know."

While Smith ranks 30th in the league with 5.94 yards per attempt, Tannehill is 34th among 35 qualifiers at 5.17 and his passer rating (76.1) ranks 29th.

The third-year pro, whose 39 TD passes are one shy of Don Strock's total for fourth in Dolphins history, continued having problems with deep-ball accuracy and holding the ball too long last Sunday. He took four sacks after leading the NFL last season with a franchise-record 58.

"I haven't been at my best," Tannehill said. "It has got to change, and it has got to change fast. I look forward to going out Sunday and changing it."

The good news for Tannehill is that Pro Bowl center Mike Pouncey practiced this week for the first time since undergoing hip surgery in July. It's unclear if he'll play or Samson Satele will keep starting in his place.

The status of Chiefs safety Eric Berry is also uncertain due to a sprained ankle suffered last week, though it appears less serious than the one Charles has. Ron Parker moved from cornerback to safety when Berry got hurt and could start for the Pro Bowler.

"We have a few injuries but we don't slow down on that," Reid said. "... Football is a joint effort. It's a team sport. Everyone's got to step up and do their job just a little bit better, coaches included."

Miami has taken the past three meetings, most recently winning 31-3 at Kansas City in 2011.