Five Bills to watch in Friday's preseason opener

May 28, 2014; Buffalo, NY, USA; Buffalo Bills quarterback EJ Manuel (3) rolls out to pass as Bills offensive coordinator Nathaniel Hackett looks on during organized team activities at Ralph Wilson Stadium. Mandatory Credit: Kevin Hoffman-USA TODAY Sports

One day after the rest of the AFC East teams kicked off their preseason, the Buffalo Bills will take the field against the Carolina Panthers on Friday.

All eyes will be on the quarterback situation as Matt Cassel is the presumed starter, but all three should see plenty of time on the field tonight. The same goes for a depleted running back group with injuries to Fred Jackson and Anthony Dixon.

These five players are worth keeping an eye on during Friday night's preseason opener.

Matt Cassel/Tyrod Taylor/EJ Manuel

Matt Cassel will get the start, but head coach Rex Ryan was unsure how much he, or the other quarterbacks, would play. Cassel has been the leader throughout the entire preseason, with Taylor working as his primary backup. Manuel is widely viewed as the third-string quarterback, but Friday night will give fans a better idea of where he stands. All three have had good days and bad days -- as you'd expect from somewhat mediocre quarterbacks -- leading to more confusion for Ryan and the coaching staff.

Ronald Darby

At cornerback, the Bills have a handful of questions. Veteran corner Corey Graham has moved to safety, while Leodis McKelvin has been sidelined for entirety of training camp with an ankle injury. McKelvin's status for the season opener is still up in the air, thrusting rookie Ronald Darby into the starting lineup. Darby was taken in the second round of the 2015 draft out of Florida State, and could pay big dividends early on if he plays well. Rookie cornerbacks typically take a little while to adjust to the speed of the NFL, which is what makes the talented Darby must-watch on Friday.

Karlos Williams

Another Florida State rookie is set to make his NFL debut on Friday, with that player being running back Karlos Williams. As mentioned earlier, the Bills have suffered a handful of injuries at running back, losing Jackson and Dixon for several weeks. In steps the rookie Williams, who was a dynamic back at FSU. He and Bryce Brown, who's had fumbling issues, should lead the way in the backfield in what should be a heavy dosage of the rushing attack behind McCoy.

Cyrus Kouandjio

Second-year offensive lineman Cyrus Kouandjio has gone through a completely different training camp this year than a year ago. He struggled mightily last season, playing in just one game with zero starts. Now, he's in line to compete for the starting job at right tackle. The massive Alabama product has improved greatly this offseason through workouts and a bigger commitment to refining his craft, and it'll be on display against the Panthers Friday.

Corey Graham

Graham is no longer seen as a cornerback for the Bills as he's made the move to safety. He's embraced the challenge of playing a new position, and has reportedly played well thus far. He'll compete with Duke Williams and Jonathan Meeks at safety, two younger players will far less experience than Graham. On Friday, the coaching staff and fans will both get a look at what to expect from Graham at safety after he proved to be a solid corner in the NFL.