Context
I work at a large Dutch, not-for-profit, partially government backed organization for 2+ years and have (in my eyes) favorable working conditions like a permanent contract, a pension, holiday leave and WFH support.
Recently I got an unofficial offer1 from a small startup operating in the same field as my current employer. One could say that the startup is operating in the "corner" of that field, while the current employer has a more encompassing and multi-disciplinary approach.
While I'm satisfied with the certainty and stability at the my current job (through the permanent contract), the startup is attractive due to the lack of bureaucracy and overall small scale. I don't want to switch jobs entirely (and lose the certainty in times of COVID) and want to investigate a 50/50 arrangement where I both work at the current job and the startup for e.g. a year.
The startup is fine with that, but I don't know if my current employer is. I need to find that out before I start discussing an offer with the startup.
Currently I have colleagues who work part-time, but their other employment is often academic (professor, PhD), not another business.
Concerns
- I'm afraid bringing up the topic of a 50/50 arrangement with my current manager will be detrimental for the work relation, it might sound as if I'm trying to resign.
- If I end up rejecting the startup offer and stay 100% at my current job, I'm afraid that my growth would be hampered as I've shown "disloyalty".
Question
How can I bring this up with my manager without sounding "threatening" or "disloyal", but indicate that I'm just exploring possibilities to enrich my career?
What I've found so far
I found this question which is slightly similar, but it deals with certain resignation in the future, not with the exploration of a possibility of partial resignation.
1: There's nothing on paper, no numbers were named, but an indication was made that they were willing to match my current salary.