It depends on how it is slowed. This is not a scalar.
The bottom line is that equilibrium must be obtained to maintain a stable orbit. So if the orbital tangential speed is decreased without changing any other factors, the corresponding centrifugal acceleration will be lower. Given that the masses of the two bodies (sun and planet) have not changed the gravitational force has not changed, so the planet will 'fall' towards the sun.
It is why skylab is no longer intact. It slowed down. Came home.
Agreed. Was being a bit silly with my post. Should have qualified that.
BTW, as you impart energy into a satellite to lift it to a higher orbit, the satellite's velocity decreases.