Silkmen manager Keith Alexander was cautiously optimistic with his acquisition and told the club's official website: "Greg brings us a bit of quality. He's shown he has an eye for goal in his time on loan in non-League.
"He's a bit of a gamble, but so is any signing, but he's featured in the Championship this season and pace is a vital commodity at this club. Hopefully he can prove himself, get into the team and improve us."
Striker Sappleton, 19, left the Foxes by mutual consent on Friday. He joined the Silkmen on loan earlier in the season and has scored six goals in 17 appearances.
Alexander was pleased with the signing and added: "Ricky has come in on loan and done well for the club. He's only 19, which is easy to forget, and now we've got 18 months now to really work with him.
"He's still young and has a lot to learn. He's a big, strong lad, didn't have a pre-season and has had a couple of injuries with us. (But) he has a good scoring record so I'm delighted with the signing."