A key defender, Joy has seen a specialist about his injured knee and had an MRI scan, and Southern United coach Mike Fridge said Joy was a definite non-starter.
Another defender, David Hayman, will also not be available due to university exam commitments.
However, the Southern squad has increased in size with the return to Dunedin of striker Alistair Rickerby, and utility Jude Fitzpatrick, but neither is likely to be up to speed for the derby match against Canterbury.
Better news is the availability of Cam Attwood and Andrew Ridden.
Striker Josh Stewart has returned to Dunedin and is also available.
Fridge's dilemma will be to assemble a balanced team, and variations such as Craig Ferguson or Victor da Costa, or Attwood - back from suspension - could feature in Southern's defence.
Ridden had a strong match for Southern's Youth side last week, and another option tried was Mike Neavison at left fullback.
Fridge was expecting a tough battle against Canterbury.
''Virtually three defenders out - Joy, Hayman, and Fitzpatrick - is not the best lead up to any match, never mind Canterbury, which did well last week to beat WaiBOP United 2-nil in Christchurch last week,'' Fridge said.
Southern had a 2-1 win over Canterbury in a pre-season match in Timaru, reversing a trend of four wins out of four for Canterbury in the past couple of seasons.
Canterbury has scored 11 goals to Southern's two in those games.
Newcomer Eder Franchini has impressed in midfield and in his normal role as linkman, Da Costa can be more than effective.
Tom Jackson is again likely to lead the attack with support from any of Taylor McCormack, Tim McLennan, Morgan Day, Josh Stewart or Tom Connor.
In the WaiBOP win, Canterbury's captain, Tom Schwarz ,scored his first premiership goal to open the scoring with a typical header from set play, and new signing from Waitakere, Dylan Stansfield (20) scored with a header from a short corner.
Two headed goals signal a warning for Southern defenders.
Fridge said his players had tosoak up any pressure put on them.
''Derby matches produce their own special sort of pressure. But we have shown that we can compete physically, and improve as matches go onwards, so I am confident that if our discipline is good and we play the football we are capable of playing, we can give them a game.''
Southern Utd v Canterbury Utd
Christchurch, today, 2pm
Southern United: (from) Tom Batty, Liam Little, Ross Howard, Craig Ferguson, George Milne, Eder Franchini, Tom Jackson, Victor da Costa, Tim McLennan, Taylor McCormack, Tom Connor, Morgan Day, Nick Hindson, Mike Neaverson, Cam Attwood, Jude Fitzpatrick.
Canterbury United: (from) Danny Knight, Dan Terris, Julyan Collett, Tom Schwarz, Mark Peers, Miles John, Mario Hofmann, Roussin Nkoy, Andrew Barton, Andreas Wilson, Dylan Stansfield, Thomas L-Boss, Stu Kelly, Shawn O'Brien, Adam Highfield, Cory Mitchell.
