The 49ers allowed the fewest passing yards per game in the NFL last season at 169.2, and yet the Super Bowl runner-ups could be looking at changes to their secondary.

Safety Jimmie Ward is set to become a free agent, and might be too expensive to bring back with his injury history. Cornerback Richard Sherman proved he still is elite but is entering the final season of his three-year contract and turns 32 years old this month. Behind him, San Francisco is full of question marks at cornerback.

Could cornerback Ronald Darby be an answer in free agency? ESPN's Ben Linsey seems to think so.

The 49ers have just under $17.9 million in salary cap this offseason. They have to make a decision on Ward and free-agent defensive lineman Arik Armstead, as well as discussing contract extensions for tight end George Kittle and defensive tackle DeForest Buckner. But Darby shouldn't cost much, mostly because he was bad at football last season. Linsey believes the former second-round draft pick could return closer to his usual form in 2020, though.

Pro Football Focus gave Darby a low 41.0 coverage grade last season, one of the worst in the NFL. Prior to last season, however, he had never graded worse than 68.3.

"The 49ers could take a shot on him as their outside cornerback opposite Richard Sherman and hope that prior form returns," Linsey wrote.

Simply put, though, Darby is trending in the wrong direction. As Niners Nation's Kyle Posey noted Monday, Darby's snap numbers have gone down every year since his rookie season. He played 914 snaps as a rookie when he had two interceptions and 21 passes defensed for the Buffalo Bills, to just 506 for the Philadelphia Eagles.

Darby never has played all 16 games in a season and has averaged only nine games per season over the last three years. He is only 26 years old, but the injury bug has taken a chunk out of him. The stats are against him, as is his health.

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Adding a veteran cornerback to the mix could be a priority for the 49ers this offseason, especially if they have put Ahkello Witherspoon in the rearview mirror and don't fully trust Emmanuel Moseley yet. On a cheap "prove it" contract, Darby might be worth the risk.

Anything more than that, however, shouldn't be thrown his way.