I am a software development student and I have got a job at a Hardware Company which also makes Software. Currently I have an internship elsewhere and I work there on Saturdays. We work in a team of four man, me and two other people work on another project and the coworker in question is there to develop features and to fix bugs in the other project.
We work in a really small office and I sit next to the coworker. In the past few months I have noticed he doesn't do anything work related, he is not programming at all. He is only playing videogames, checking the news and his social media. And now it's really to start bothering me because a few things. Our manager, he only works on mondays till fridays so he is never in the office when we are working, he trusts us.
Also as we are developers, we use programs he doesn't know anything about. He doesn't really know the source control software and such so he has no idea what is done and what isn't, the only times he comes to check in he is easily happy if one bug is fixed which should've took him a few minutes.
I am thinking about bringing this to the manager soon because it might be a problem for me too in the future if I can't go work more days after graduating because the manager thinks the coworker in question is a resource for him to develop and fix bugs.
Should I first tell the coworker himself that he should be more motivated to actually do his work and that he needs to do something with his paid time or what should I do?