"The worker" is not accepted. It seems like it should be since "The employee" is. I know it is starts with mit and people are saying it basically means "with" + "worker", therefore coworker, but I read it more like "with work" + er, or one who is with work, ie. someone who has a job. I could see if employee wasn't accepted, I just don't see how employee is, but worker is not.
In English, a worker is anyone who works(as opposed to an aristocrat who does not need to work). "He is a real worker", could be said of a man who works very hard, either on his own account(self-employed), or as an employee: An employee is a person who works for someone else or for a firm. A co-worker in English tends to denote a (scientific) collaborator on a project and a colleague is a person(usually of similar status?) who works with you in the organisation.