Definitely not. That person is obviously not being stimulated enough physically or intellectually and clearly needs to be either given more tasks, along the same lines, or pushed up a level to train for something else that will be more challenging for him.
The problem with too many workplaces is that they expect everyone to be sheep, going at exactly the same pace, and doing everything in a prescribed manner. There is little room for initiative, innovation, or difference under the stifling culture of conformity. In this type of atmosphere, it is often difficult for mavericks, or people with different ideas and perceptions, to thrive.
Yet workers are not clones of each other. Just because they are in a team does not mean they should all go at exactly the same pace in their work like robots or automatons. This guy is clearly bored, having finished his work, and so does the next best thing to relieve it – take a nap to escape the tedium of his day. The important thing is that he has done his work, exactly as expected, and is giving a huge message about his abilities and expectations by then switching off into his own world. He is pointedly making a statement that if his ability is not going to be recognised, he’s going to do what is directed, and nothing else.
Some people might have asked for more tasks, but he deliberately hasn’t done so as he wants his abilities to be acknowledged and reinforced. There are tons of workers like that who know they can manage more challenging tasks, or new responsibilities, but are not given the opportunities to do so, for whatever reason, and who are essentially voting with their feet. They might be there in body, but any real commitment to what they doing would be missing.
A good manager or team leader DEVELOPS his/her staff so that they are working to their potential and can feel good about their own contribution. A leader does not fire workers who are clearly doing their job and are bored witless with not being challenged or stimulated enough in what they are being assigned. Time to see what would motivate this worker to stop him sleeping by reviewing his progress as necessary and negotiating a new way forward where he can feel valued, occupied and proud of his efforts,
This worker needs to be set regular targets which become more challenging after every completion. In that way he won’t have time to be dozing, and you would also be doing your job as a manager in making the most of his talent, enthusiasm and skills, at his own pace, and increasing his opportunities to grow.