Medical student being cut out of a project by fellow unbeknownst to supervisor
You should tell your supervisor you were disappointed there was not more work for you to do.  This will ensure your supervisor knows your viewpoint.  There's no need to suggest that the fellow was deliberately preventing you from contributing.  It's not clear what the fellow's motivations were, so it is hard to be sure if they should be discussed.  Stick to your own actions, which are directly relevant to your reputation.