But these days the injury-prone 31-year-old strike bowler has to do more than just prove his fitness.
With the arrival of Neil Wagner and Ian Butler, the development of Mat Harvie and, more recently, Anthony Bullick, Otago's pace bowling stocks have swollen and competition for places is intense.
McMillan suffered a hamstring strain earlier in the summer but has been fit for the past month and has had to bide his time waiting for an opportunity.
That chance might come today when Otago plays Auckland in an away Plunket Shield match.
The Volts have made two changes from the side which beat Wellington by nine wickets in Queenstown last week.
Both Sam Wells and Butler are unavailable due to injuries.
McMillan makes the 12 for the first time this summer and experienced medium-pacer Warren McSkimming returns after being rested in the last match.
Butler, who has a mild side strain, was due to be rested anyway with Otago opting to rotate its pace bowlers this season.
But Wells has injured his shoulder and may be out until the New Year.
The injury has come at an unfortunate time, with the University-Grange all-rounder enjoying a tremendous patch of form.
He has taken 14 wickets, including two five-wicket bags, and scored his maiden 100.
His bad luck has paved the way for McMillan to return.
"There are a lot of young guys coming through now, which is good to see," McMillan said.
"They've been bowling really well, so it is up to me now to get out there and perform or else you never know what will happen there."
When the experienced strike bowler is fully fit he is one of the fastest bowlers in the country.
But injuries have robbed the right-armer of some of his prime years.
Since making his debut for the province in 2000-01, McMillan has played just 37 first-class games.
He spent the entire summer of 2003-04 on the sidelines with a stress fracture in his back and a shoulder injury brought a premature end to the 2004-05 season.
McMillan is by no means guaranteed to play today.
With Wagner, Bullick, McSkimming and Harvie also competing for a place in the XI, McMillan may find himself carrying the drinks.
But whether he gets the nod or not, he is feeling confident.
"I've been bowling pretty well in club games and bowled pretty well for Otago A against Canterbury A."
Auckland is anchored at the bottom of the table, pointless after four matches.
The selectors have not pushed the panic button with most of the personnel returning from the side which lost a rain-affected clash with Northern Districts by 55 runs.
Scott Styris has a shoulder strain and will be rested and Lance Shaw is still struggling with a heel injury and will sit out the game as well.
Jeet Raval will replace Styris and offspinner Bhupinder Singh is back in the 12 to provide another spinning option.
Coach Paul Strang has urged his side to concentrate on the basics and get back to playing the sort of cricket which enabled it to win the four-day competition last year.
"We've just got to really focus on all the elements that will allow us to perform well, and often that's making sure that you do all the small things right," he said.
"If you get those spot on then everything tends to come together."
Otago v Auckland
Colin Maiden Park, from today
Otago: Craig Cumming (captain), Nick Beard, Derek de Boorder, Neil Broom, Anthony Bullick, Shaun Haig, Mathew Harvie, James McMillan, Warren McSkimming, Leighton Morgan, Greg Todd, Neil Wagner.
Auckland: Gareth Hopkins (captain), Richard Jones, Ravi Bopara, Reece Young, Anaru Kitchen, Jeet Raval, Andrew de Boorder, Tarun Nethula, Greg Morgan, Michael Bates, Pieter Erasmus, Bhupinder Singh.
