McMillan has played 40 first-class matches for the Volts and taken 95 wickets at an average of 35.28.
Arguably, he had his best season in 2006-07 when he claimed 23 wickets at 26.82, including a career best of seven for 105.
But the past three summers have been hard slog for the 32-year-old and he looks set to lose his contract, with promising paceman Anthony Bullick the most likely replacement when the contracts are released next week.
At his best, McMillan was one of the quickest bowlers in the country, but a frustrating run with injuries meant he spent a lot of time watching from the sideline.
He shortened his run-up in 2008 to help reduce his susceptibility to muscle strains, which have plagued his career.
As a shoulder bowler, he was still able to generate good pace with his effort ball, but his 140kmh deliveries were mixed in with plenty of medium-pace fodder.
McMillan played just three first-class games last summer, taking five wickets at 60.40, and did not feature in either the one-day or twenty/20 tournaments.
Given his limited contribution, it would be hard for the selectors to justify offering him a provincial contract.
Seamers Warren McSkimming and Neil Wagner are almost certain to retain their contracts, while left-arm spinner Nick Beard impressed in his first full season for Otago.
With paceman Ian Butler returning to the Otago fold after losing his national contract, there is probably only room for one more specialist bowler.
Fast bowler Mat Harvie, another player whose career has been hampered by injury, did not declare his availability and was not considered.
That has paved the way for Bullick.
The 25-year-old is brisk rather than express, but he improved with each outing for Otago and was the leading wicket-taker for the province in the one-day tournament, with 14 wickets at 14.71.
He also has the potential to develop into a useful lower-order batsman.
All-rounder Sam Wells is set to join Bullick, after some outstanding performances in the Plunket Shield.
Wells' future is probably more as a batsman who bowls a bit, but last summer he surprised with his ability to swing the ball.
He took 21 wickets at 24.42, including two five-wicket bags, and he finally demonstrated his potential with the bat, cracking two centuries and three fifties.
Ink in the names of wicketkeeper Derek de Boorder and leading batsmen Craig Cumming and Aaron Redmond, while former Black Caps batsman Neil Broom will take the spot vacated by the Auckland-bound Greg Todd.
But top-order batsman Leighton Morgan's contract is in peril.
He could be squeezed out by Darren Broom.
Broom - Neil's younger brother - scored a century on debut and also help North Otago lift the Hawke Cup with a superb knock of 133.
