ORCHARD PARK, N.Y. -- Stephon Gilmore was routinely the best player on the Buffalo Bills' practice field during training camp. Halfway through the regular season, the team's top cornerback has become one of its biggest defensive liabilities.

The low point for Gilmore came Sunday in the first quarter of a 41-25 loss to the New England Patriots, when former Bills receiver Chris Hogan streaked down the left sideline and caught a 53-yard touchdown pass from Tom Brady in stride. Even before Hogan crossed the goal line, a trailing Gilmore was turning back across the field, seemingly searching for whichever teammate blew his assignment.

Blame, however, should apparently fall on Gilmore. On Monday, coach Rex Ryan called the play a "big mistake" for the fifth-year cornerback whom Pro Football Focus now ranks a disappointing 82nd in the NFL among players at his position through eight weeks of the season.

Bills CB Stephon Gilmore, who is a free agent after this season, is the 82nd-ranked cornerback in the NFL through eight weeks, per Pro Football Focus. AP Photo/Bill Wippert

Reminded Monday of how Gilmore has slipped since his lights-out play in training camp, Ryan nodded before looking down and shaking his head. The fall of one of Ryan's most promising players had apparently left the coach bewildered.

"I think it is just getting back to the fundamentals and what he did in training camp," Ryan said. "He was physical, he was aggressive, and if the ball was thrown his way you were wondering if he was going to come down with it."

The same was true last season. Gilmore was the NFL's 14th-best cornerback as rated by Pro Football Focus, and his 20 passes defensed ranked fourth in the league. The strong performance justified the Bills' decision during the offseason to exercise Gilmore's $11.082 million fifth-year option for the 2016 season while also raising the bar in negotiations for a new contract.

Amid talks for a new deal, Gilmore skipped voluntary offseason workouts this past spring and left the door open for a training camp holdout before he eventually reported on time in July. Hinting that he was worth as much, if not more, than the five-year, $75 million deal the Washington Redskins extended Josh Norman, Gilmore did not shy away from making a public stance about his value.

"Yeah," Gilmore said, when asked if he was in the group of elite NFL cornerbacks. "I know it."

Despite Gilmore's impressive practices in the ensuing weeks of camp, the Bills were clearly skeptical about what he was worth to them. Summer negotiations with his agent seemed to yield little common ground, and through the first half of the regular season, it's clear the Bills have made the right decision in holding off on giving Gilmore a new deal.

If the trend continues -- and Ryan acknowledged Monday that there have been ups to Gilmore's season in addition to his downs -- the Bills won't have a hard choice to make in February as they contemplate whether to open their wallets and keep Gilmore around. Not only would the franchise tag make little sense given Gilmore's play this season, but a contract extension at the level Gilmore has been seeking would be silly, too.

Given the current course, the Bills would be wise to let Gilmore walk away.