PHILADELPHIA (973espn.com) - The big money wasn't there for a talented 25-year-old cornerback in free agency and the reason why was obvious.

Since being acquired from Buffalo before the 2017 season for receiver Jordan Matthews and a third-round draft pick Ronald Darby has missed 17 of a potential 37 games with the Eagles, including the final nine of last season -- seven to close the regular season and two playoff contests -- with a torn ACL suffered against Dallas on Nov. 11.

After a visit to Kansas City, it was clear to the Darby camp that the injuries -- a dislocated ankle in 2017 and the ACL -- brought the price down and kept Philadelphia involved. The Eagles were able to land Darby a prove-it deal that could be worth as much as $8.5 million with incentives.

The real numbers include only $4.5 million fully guaranteed, which comes in the form of a $3.5M signing bonus and a $1M base salary, with the other $4M tied up in per-game roster bonuses, as well as playing time and production.

From Darby's perspective, the lack of an offseason due to the rehab process would have made it difficult to assimilate to a new defense quickly so by returning to Philadelphia where he already understands the landscape and what defensive coordinator Jim Schwartz wants will enable him to hit free agency again in 2020 at 26.

"Of course it’s been real frustrating," Darby admitted on a conference call with Philadelphia-area media on Tuesday. "I never got hurt like this before until I got to Philly. So this was new. Everything was new to me. But I’ve been playing football since I was 8 years old. I’ve just got to have a healthy season."

In theory, if Darby holds up for 16 games or at least near it in 2019 and proves the ACL is in the rear-view mirror, the really big money on a multi-year deal will be there.

The immediate goal is Week 1 and a return to being one of the starting outside CBs.

“My rehab is going great right now,” Darby said. “I’m hitting all the marks I need to. My goal is to be back by Week 1.”

The status quo would be Darby at right CB opposite Jalen Mills, who is also going through rehab after surgery for a foot injury. From there the Eagles hope third-year CBs Sidney Jones and Rasul Douglas can push for playing time outside while Avonte Maddox and Cre'Von LeBlanc handle the slot duties.

“I always wanted to be back, of course,” Darby insisted. “It’s hard to walk away from a place like this.”

-John McMullen covers the Eagles and the NFL for 973espn.com. You can reach him at jmcmullen44@gmail.com or on Twitter @JFMcMullen