A year ago, I finished my Master's degree and ended 6 months of working for an incredibly manipulative and demanding supervisor. We started working on a publication of my Master's results, which is awaiting final approval (post-corrections) at the journal we submitted to.
Last week, I read a paper this supervisor had published recently, which had a figure taken directly from my Master's dissertation. Our in-press article wasn't cited, and I wasn't co-author, referenced, or even mentioned in the acknowledgements. No direct reference was given for the figure, but the text surrounding it made it sound as if it had come from another article by my supervisor from last year.
It seems pretty clear to me that this is plaigarism - we worked on this project together, certainly, but the final product was a result of my work and their guidance.
My problem is, I don't know how to deal with it. We are currently co-authoring a paper, so I don't want to cause a rupture. I also plan to continue working in this field, and would like to avoid having a senior researcher and previous supervisor to be angry. At the same time, I don't want them to get away with using my work, and taking all the credit for it.
I will certainly tell them that I feel uncomfortable with how they used my work, but realistically, what can I expect/hope to happen here?
UPDATE - the figure in question is an overview of a simulation model I created, so is pretty much the core part of my Master's work.