The 23-year-old, who has appeared in the colours of Rushall Olympic and Solihull Moors so far this season, has linked up with the Pilgrims following Ben Middleton's recall to parent club Harrogate Town.
Middleton (22) was set to spend a second month on loan with the Pilgrims — but has been recalled by manager Simon Weaver just six days after signing an extension.
Atkinson is eligible to make his United debut in Saturday's home clash against Blyth Spartans.
Fellow defender Brad Beatson (21), meanwhile, has linked up with former club Gainsborough Trinity on an initial month's loan.