The forward was last with the club in 2014 before he moved to Kings Lynn. Since then, Gregg has spent time at Tamworth, Boston United, Brackley Town and Stamford.
In his previous 89 appearances for the Gingerbreads, Gregg has bagged 32 goals.
Paul Rawden was happy to get Gregg in "We know that having a fully fit and happy Gregg gets us goals at this level. Before signing him, we've told him what we want and expect from him when he pulls on the shirt. He's a handful for any defender and will bring a real presence to our forward line. Also, he's a Grantham lad and wants to do well."
Gregg added "It's good to be back, there are plenty of faces around the club that I know really well. I'm looking forward to the new season and getting some goals!''