1. Depends on the country and state as to what laws are in effect.
2. For the UK, there would have had to have been a return to interview work first to determine if the employee was fit to return to work and if so, whether or not they were capable of resuming all their duties full-time or if a phased return to work was required - and how they were to be monitored on return to ensure that they were not being placed at risk due to incomplete recovery from injury.
Why was the employee in question placed on light duty? How was this assessed - by a medically qualified person, by discussion and agreement (between who?) etc?