I work at a relatively small company that provides a team of developers and a project manager/product owner for a project as consultants to another small company. I'm working on the project full time. Both companies are in Europe.
Recently, my boss contacted me that the client company wants to make me an offer to change companies. He told me that if I strongly felt like changing, that would be ok. At the same time, he emphasized that he wants to keep me. Quite some time was also spent by him down-talking the opportunity and giving me a very short time window to make a decision. The exact content of that offer is not clear to me, but the responsibilities would likely be the same as I have now. Before those talks there were also talks of an opportunity for a role change within my company that might realize in a few months.
I like to work at my company, but I'm naturally curious about that offer. I could also imagine to work for the client company directly in the future. My concern is that if I explore that offer, my chances for the internal opportunity might be lowered. At the same time, I somehow feel like I owe the client company at least a statement that I appreciate the interest.
How can I proceed in a professional manner without lowering the chances for internal opportunities and without burning bridges at the client company?