Cleveland ? Kellen Winslow Jr.’s use of a motorcycle might have violated standard NFL contract language that prohibits players from engaging in dangerous activities.

The Cleveland Browns could require Winslow, who lost millions last year because of a season-ending injury, to pay back a $4.4 million signing bonus he received in March.

The 21-year-old tight end sustained internal injuries and damage to his right shoulder and right knee in an accident that sent him flying over the handlebars of his newly purchased motorcycle.

Winslow was being treated at the Cleveland Clinic, where the team’s medical staff was waiting for swelling in the shoulder and knee to subside. The team declined Tuesday to provide an update on his condition.

NFL spokesman Greg Aiello said the standard NFL contract forbids players from taking part in any activity “which may involve a significant risk of personal injury.”

Winslow’s rookie season ended when he broke his right leg during an onside kick in Week 2.