Lawrence Okoye has described taking part in minicamp practices with the San Francisco 49ers as the hardest thing that he has ever done.
The British discus record holder took more snaps that any other defensive lineman during off-season practices with the Super Bowl runners-up.
The 21-year-old told the Sacramento Bee: "It's the hardest thing I've ever done, I'm under no illusions."
The 49ers' defensive coordinator Vic Fangio added: "He hasn't had anybody hit him yet. He hasn't had a double-team yet. He hasn't figured out if it's a run or pass, whether he should rush or play the run. So it'll probably be a very slow process with him much more than a normal rookie."
The Olympian announced his intentions to move to the NFL earlier this year, despite having never played American football.
