Lucas planned to give Han a minor appearance and a single line of dialogue informing Yoda about General Grievous’ whereabouts, but no larger role was planned.
Concept art was made of young Han, but the scene was never filmed or progressed any farther than the initial sketch, as it would have muddied the storyline.
Han is very skeptical about the Force in the original trilogy, which would have seemed odd if he had known Yoda, one of the most powerful Jedi to ever live.
His prequel appearance was going to reveal that young Han was taken care of by Chewbacca, which countered the then-canon EU that stated he saved Chewbacca from a slave colony.
The prequels already included many characters from the original trilogy, including Chewbacca, so adding Han would have likely only complicated an already somewhat confusing timeline.