Jim Harbaugh has described Lawrence Okoye as "not a good football player" following his first practices in pads with the San Francisco 49ers.
The British discus record holder put his athletics career on hold to join the Super Bowl runners-up, despite having never played a down of gridiron football.
Speaking at a press conference, the 49ers head coach said: "He's not a good football player, and his next growth is to be not a bad player, but he's made growth from never having played the game of football so, once again you talk about process, the expectations need to be realistic and that's the next step.
"I want him to be a bad football player because that's the next jump up for Lawrence Okoye, but he's making significant strides each and every day."
Okoye, who is expected to play as a defensive end, added: "I should be knocking guys down, but they're knocking me down, and I should be getting better leverage. Everyone in the organisation has been so good in giving me advice and encouragement. I want to do it for them and me."
The 49ers face the Denver Broncos at Candlestick Park in their opening pre-season game later today.
