The explosive English all-rounder injured his foot during Otago's three-wicket loss to Auckland on Monday and Sam Wells has been added to the squad as cover.
Mascarenhas starred for Otago in its last outing with an undefeated 75.
He demonstrated his awesome power-hitting ability when he smacked five sixes off one over from former Black Caps strike bowler Daryl Tuffey.
But with the Otago top order going so well, Mascarenhas has had little opportunity with just two innings for the province.
The team might have to rejig its order to take more advantage of his boundary hitting exploits.
He has also been economical with the ball, going for 3.61 an over.
His team-mates, Warren McSkimming and Craig Cumming, have been equally miserly.
Otago will lose the services of its New Zealand duo, Brendon McCullum and Neil Broom.
Broom is poised to make his international debut in the fourth ODI against the West indies today, with injury-plagued all-rounder Jacob Oram ruled out with a damaged Achillies tendon.
The in-form Shaun Haig will return to his spot at the top of the Otago order for McCullum and Hamish Rutherford will replace Broom in the middle.
Despite the disruptions of the New Zealand players coming and going, Otago skipper Craig Cumming said the side was in good heart and looking forward to the second half of the tournament.
"I always think the first round is about keeping yourself in the mix and this is the round that really counts," he said.
"So it really starts now. We're in the right position and the right part of the table, but we've got to play well to make sure we stay there."
Otago is coming to the end of a stretch of three away games, but Cumming said the team was feeling refreshed after a deep-sea fishing trip on Wednesday.
"It was a real refresher for us. You do get a bit sick of motel rooms, so that was a great distraction. Guys were jumping around talking about the one that got away this morning and there is a real buzz in the camp."
Northern Districts has a settled look, with just Black Cap batsman Daniel Flynn unavailable while on national duty.
The Marshall brothers, James and Hamish, remain key wickets for Otago, and BJ Watling has been in good touch.
He has scored 258 runs at 86 in five innings.
The bowling attack is well balanced, with spinner Bruce Martin and left armer Bradley Scott experienced campaigners.
All-rounder Joseph Yovich is having a good season with the ball and promising left arm quick Trent Boult is a name to look out for in the future.
State Shield teams
Otago (from): Craig Cumming (c), Aaron Redmond, Shaun Haig, Greg Todd, Hamish Rutherford, Dimitri Mascarenhas, Nathan McCullum, Derek de Boorder, Ian Butler, Neil Wagner, Craig Smith, James McMillan, Sam Wells.
Northern Districts: James Marshall (c), Hamish Marshall, BJ Watling, Michael Parlane, Kane Williamson, Peter McGlashan, Joseph Yovich, Bruce Martin, Bradley Scott, Brent Arnel, Trent Boult, Greame Aldridge.
