Actually it could be either. "Skilled" means that a person has the ability to perform a task, AND usually implies that this skill has been learned through training. "Skillful" means that a person has the ability to perform a task, BUT normally this is a natural ability. So, in your example 'skilled' is the probably the best choice because you said the worker is experienced, and presumably they have learnt this skill as a result of this experience.

He is called a skilled worker.