McCullum and de Boorder have joined the New Zealand A team on the tour of the UAE and Ryder was meant to travel with them but pulled out of the trip earlier this week because of personal problems.
He also missed Otago's match against Canterbury at Hagley Oval on Sunday but has been named in the line-up for today's must-win match against the Canterbury Kings at the University Oval.
Otago coach Dimitri Mascarenhas did not return calls. Assistant coach Nathan King said Ryder was available to play but would not comment on whether Ryder was over his personal problems.
De Boorder's absence means Michael Bracewell will take the gloves. He has performed the role for the province in the past and kept wickets all through school.
McCullum's absence will also be sorely felt. The off-spinner has formed a mostly frugal combination with fellow spinner Nick Beard during the middle overs and has batted has high as No 4.
Seamer Jacob Duffy has been struggling to find his length and has been dropped for the match. With just the one wicket and an economy rate of 10.80, the selectors had little choice.
Former Central Districts all-rounder Roald Badenhorst and batsman Brad Rodden have been named replacements. Badenhorst has been in good form with the bat for Albion, whacking a couple of centuries.
''He has been scoring a lot of runs in club cricket and ultimately that is why he is in the team - sheer volume of runs,'' King said.
''We see him as one of our next best bats and that is why he has come into the team to do. He obviously has another string to his bow with his bowling and he might get an opportunity with the ball.''
Rodden is more of a first-class player at this stage of his career but has answered the SOS. Between Black Caps duties and New Zealand A commitments, Otago has been stripped of a lot of talent.
''We are here to promote our players into the Black Caps and New Zealand A environment ... so to have seven players away with both teams is a great result for Otago cricket. But it makes it challenging in terms of the players that remain here to still win games of cricket for the Otago Volts.
''We've just got to make sure we keep bringing players through the system and continue to be a successful team in the process.''
With just one win from six twenty20 games, Otago's chances of making the playoffs are fairly remote, King conceded.
''There is still a mathematical chance I belief but you'd have to rely on other results. But it is too far out to know how it would all work, so at this stage we've just got to keep winning and see what happens.''
