Master Systems Display (MSD) artwork by Rick Sternbach for U.S.S. Pegasus NCC-53847 created for the Star Trek: The Next Generation episode "The Pegasus" 1994.
According to Rick Sternbach, the producers originally intended to create a new starship design for the episode. In a post on TrekBBS, Sternbach writes:
As far as the Pegasus was concerned, yes, there were a few sketches of a ship done, but to make it easy on the VFX folks it was supposed to be a kitbash of sorts from either a Nebula or an Ambassador ( I don't have the sketches handy, so I can't recall exactly).From this sketch, it's clear that the U.S.S. Pegasus was meant to be a kitbash of the Ambassador class. Instead of building a new model, the U.S.S. Grissom model from Star Trek III: The Search for Spock was re-painted and the U.S.S. Pegasus became an Oberth-class starship.