Dolphins land fifth-round RB Jay Ajayi, whose knee caused draft slide

Watching Jay Ajayi bowl his way through mostly helpless Mountain West defenders on his way to more than 2,300 yards from scrimmage last season, it was easy to ask early in Round 5 ... why is this guy still available?

The biggest reason: a knee that some NFL team doctors believe might not hold up long in the NFL. A few weeks ago, reports surfaced that his knee was essentially bone on bone despite being able to play — and play every game — the past three seasons.

Could Ajayi be the next Cadillac Williams — an energetic, feisty, powerful runner with awareness and instincts who never can stay healthy? That's what some teams feared, which precipitated his fall to the 149th pick, where the Miami Dolphins took a gamble on potential greatness.

It's not a stretch to say that Ajayi has some Marshawn Lynch-like capabilities, but it is a real projection to say that Ajayi is going to have anywhere near the longevity that Lynch has. If healthy, Ajayi could be a great power complement to Lamar Miller in the Dolphins backfield and give Ryan Tannehill an underrated receiving outlet who had 50 catches and four TDs last season.

But the fear clearly is that Ajayi's brilliance could be short. If he's the rare back who can sustain a pounding — he's not that elusive a runner — and play through what looks to be a very balky knee, the Dolphins will have hit a home run. It might have been worth the risk at this point in the draft.

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Eric Edholm is a writer for Shutdown Corner on Yahoo Sports. Have a tip? Email him at edholm@yahoo-inc.com or follow him on Twitter! Follow @Eric_Edholm