McManus is getting married on Saturday to Dunloy and Antrim camogie player Aileen Martin.
The Cushendall man played a pivotal role as he struck 1-13 in last weekend's dramatic 3-20 to 2-22 extra-time win over Carlow.
Paul Sheehan hit 0-15 for Down as they beat Roscommon 2-24 to 1-20.
However, Down's recent form suggest that the Saffrons should still be good enough to see off the Mourne County with something to spare despite McManus' absence.
SATURDAY
SUNDAY
Antrim will hope Neil McManus' absence will not unduly hinder them in Saturday's Christy Ring Cup game against Down at Cushendall.