Copyright on portfolio


Hello everyone, I have a question about making a portfolio of 3D models.

I was doing my portfolio at Artstation and the few models I have finished are creatures, robots from movies and videogames. I made the models from scratch, but since they are characters from a movie / game I don’t know if I would have copyright problems. For example i made a 3D model of a kodiak (robot from Mechwarriors)

I simply want to use them for portfolio and not to sell them. Should I put something in the publication like “i don’t own the rights”, “all rights reserved to …” or “fan art”? and if i should, what exactly is the phrase, sentence to put so i have no inconvinients?

I tried to find information about copyright but I didn’t find it specifically to use in a portfolio and I wanted to see if anyone knows about this topic to clarify this issue.