The Red Sox, coming off a record-setting September collapse, announced the moves Monday.
Wheeler, 33, appeared in 47 games this past season and was 2-2 with a 4.38 earned run average in his only year with Boston. He has also pitched for the Rays, Mets and Astros in a 12-year career.
The 35-year-old Atchison was 1-0 in 17 relief appearances for Boston, posting a 3.26 ERA. He played two seasons for the Red Sox and has also pitched for the Mariners and Giants.