ORCHARD PARK, N.Y. (AP) -- Bills running back LeSean McCoy did not finish practice Wednesday after experiencing tightness in one of his hamstrings.
Coach Rex Ryan didn't know the severity of the injury by saying the team's top offensive threat was still being evaluated by trainers. Ryan also wouldn't speculate on McCoy's playing status for Sunday, when Buffalo (4-2) travels to play at AFC East rival Miami (2-4).
''We feel good about the guys that we do have, but that's assuming he won't play,'' Ryan said, when asked how McCoy's possible absence would affect the game plan. ''We'll see how it goes.''
McCoy has played a key role in sparking Buffalo's four-game winning streak - the team's longest in eight years. It's a stretch in which he's combined for 470 yards rushing and six touchdowns, including one receiving.
In a 45-16 win over San Francisco , McCoy had 19 carries for 140 yards three touchdowns in a game Buffalo totaled 312 yards rushing, the fifth-highest output in team history.
McCoy is in his second season in Buffalo after the Bills acquired the NFL's 2013 rushing leader in a trade with Philadelphia. McCoy's production was slowed last year, when he opened the season with a partially torn left hamstring. He then missed the final two games of the season because of a knee injury.
Ryan didn't say which of McCoy's hamstrings was being evaluated.
Mike Gillislee is McCoy's backup followed by veteran free-agent addition Reggie Bush and rookie fifth-round pick Jonathan Williams.
The Bills offense could also be missing starting receiver Robert Woods, who aggravated an injury to his right foot against San Francisco. Woods was still wearing a protective boot on Wednesday.
Starting tight end Charles Clay also didn't practice after he hurt his ankle on Sunday.
Buffalo is already playing without top receiver, Sammy Watkins, who aggravated an injury to his surgically repaired left foot last month. Watkins was placed on injured reserve and is not eligible to be activated for four weeks.
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