If you look at the senior Bowl practices where one DB covers one WR man to man, he had a real hard time staying with any receiver he was to guard.

Also, he was targeted 34 times this year in games - 28 of those were completed (82%) for 479 yards and 4 TDs. The passer rating against his coverage was 118.4.

He was a lot better last year.

He chose not to run the shuttle or 3cone at the combine or his pro day.
I would guess because he knew it would be slow?
He ran 40 at 4.62, fifth from the bottom of his class.

I hope he played this year through an injury.
If he wasn't hurt this year, tape and numbers point to him not being able to cover NFL receivers.