Connecting analog power domains in the same chip in ICs (Integrated Circuits)
You don't say so I am assuming that the 3.3V domain signal is a cell that you can't touch and scale back.  Otherwise the right solutions is ... don't send a 3.3V signal into a 2.5V domain.

Using clamping diodes is problematic.  Do you know how the output driver will respond to having it's load impedance modulated like that? What about the parasitic capacitance of the diodes? What is the impact on interference from you dumping a signal onto the rail?

It would be easier (again assuming that you can't touch the 3.3V output) to convert this signal locally.  Design a simple emitter follower in NMOS (which gives you a gain of 0.8) using the 3.3V transistors and you will get an easily scaled voltage that is only two components and gets you very close 2.65 V. You could probably degenerate the source current a bit more for a nice linear inbounds conversion.  The drive will be asymmetrical but again you don't say what the speed requirements are.

Make sure you have a good path back to the driver for image current flow.