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.
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Ex-policeman Antony Lowry-Huws, 68, of Kinmel Bay, and Sheila Whalley, 70, of Abergele, were jailed in 2013 after duping lenders across north Wales.
Lowry-Huws' wife Susan, 63, who got a suspended sentence, must pay back the largest amount of £75,790.
The three were convicted of conspiracy to defraud along with two others.
At a Proceeds of Crime Act hearing at Mold Crown Court, it was agreed Antony Lowry-Huws and Whalley made £4m each from their crimes.
Lowry-Huws was ordered to repay £27,905, while developer Whalley will give back £18,350.
His wife, who was said to be on the periphery of the scam and under the influence of her husband, benefited £896,351 and must pay back £75,790.
During the trial, the court heard mortgage lenders were conned into lending thousands of pounds in mortgages on properties across north Wales, Cheshire and the north west of England.
The prosecution said the deceit was achieved by inflating the value of the property used as security, hiding that in some cases no deposit was put down, or inflating the rental income potential to make the mortgage rate more acceptable.
In some cases the homes on which mortgages were advanced did not exist.

But Tommy Refenes has done it from the comfort of his front room in America.
When his sister launched a fundraising page to help their diabetic mum buy an alert dog, Tommy took it upon himself to walk some of the largest maps in gaming to help out.
His efforts ended with a six-hour stint on Grand Theft Auto V (GTA V) as he strolled across Los Santos.
Tommy, who is the co-creator of indy game Super Meat Boy, also spent two hours and nine minutes walking across the map of Red Dead Redemption and took four hours and 19 minutes to complete the length of Grand Theft Auto San Andreas.
Below the live stream of the fundraiser, the gamer wrote that his mum "is having a lot of trouble with her Type 1 Diabetes and an alert dog could help her out and improve her health tremendously".
He added: "The dogs are trained to recognise smells due to high and low blood sugar and alert their owner.
"Mom has lost the ability to do this on her own which could be potentially very dangerous for her.
"After 32 years of having diabetes, it's becoming almost impossible for her to tell when her sugar is going low or high. This is potentially a fatal condition."
Following Tommy's efforts the fundraiser page had broken the $15,000 (Â£9,307) target by $677 (Â£420) with 112 days remaining.
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Antrim will hope Neil McManus' absence will not unduly hinder them in Saturday's Christy Ring Cup game against Down at Cushendall.
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Three people involved in one of the UK's biggest mortgage frauds, worth up to £24m, must repay some of the money they made.
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Most people associate a charity marathon with months of training ending in a gruelling test of endurance.