Debug Fortran through Matlab called exe/DLLs?

I have a Fortran code which is called in a Matlab GUI. The program runs some Matlab functions, then calls a Fortran executable to quickly perform some calculations. The results are brought back into Matlab. I would like to debug the Fortran code, however 'debugging' it in Visual Studio provides errors because the dlls/links haven't been set up for the Fortran to run on its own.

Is there a way to basically "step into" the Fortran part like you can do in the Matlab portions. Or is there a way to find how this exe is setting up the links and run the Fortran on its own?

Complicated, I know. It's not my creation, but I'm working with it now and want to understand what's being run.