Jonas Gray has said that he must work hard to impress the Miami Dolphins coaches during training camp.
The running back is preparing for his first year playing in the NFL, having spent last year on the 'physically unable to perform' list following a knee ligament tear.
The 23-year-old told the Dolphins' official website: "Every time I come out and sacrifice my body and go out and play, I've got to give it my all.
"Before the scrimmage, Coach [Joe] Philbin talked about how important it was for a number of guys and Coach [Mike] Sherman echoed those same things, so I knew I had to come out right away and play with full speed, play with detail and play physical.
"It felt good to just go around there and play physical and mentally it's really good for my knee to just know it's 100%, back to where I need to be and I'm just going to continue to work."
The Dolphins begin their pre-season with a game against the Dallas Cowboys this weekend.