Uhm ... No he couldn't. He even told cell himself that he's not strong enough to beat him. He said that Gohan is the earths last hope. That basically says it all.
Did you see the goku smile? And he did not hang on in like vs freezer where every hope was lost. Goku could have beaten cell, but wanted to awaken the potential of his son. The next generation...How dare are you to question the almighty Goku.
Goku wanted gohan to test his sleeping power against cell
he didn't even bother break a sweat. Besides we know that goku didn't even try to beat cell. And difference in power level means nothing. Goku grows in battle as seen so many times