Wheatcroft was released from his contract at Glanford Park yesterday and had been tipped to join Conference strugglers Leigh RMI.
However he instead joins Southport, who in ninth place are 11 points off the final playoff place to gain a spot in next years third division.
The 22-year-old made just four first team appearances in North Lincolnshire, and is hoping to get himself back amongst the goals at Haig Avenue.