The captain will miss tomorrow's White Ribbon game against Canterbury, due to his flight to Melbourne for international duty.
The Oly Whites, who can qualify for London by winning the Oceania qualification tournament in Taupo from March 16 to March 25, play the Frank Rijkaard-coached Saudi Arabia team at Lakeside Stadium on February 20 and 23.
"I am delighted to be included into the Oly White squad. It's been one of my targets for some time, and will be a great experience," Prattley said.
Otago United coach Richard Murray recognised the bittersweet situation, and while happy for Tristan, added his dismay at other match re-scheduling which could leave his side with a one-month gap without matches at the end of the season.
"We could overlap into the winter season, which is scheduled to start on March 31. It's a joke," he said.
More immediate problems face the coach since, apart from Prattley, in-form keeper Peter Evans is not available, Joel Stevens has gone to the US for a trial in Houston with the Earthquakes, Sam Mepham is absent on a university camp, Liam Lockhart is overseas, and Craig Ferguson is injured.
Otago's revolving door selection system thrusts in keeper Oswaldo Rodriguez for his first match of the season, while also drafted in are strikers James Govan and Donnie MacGregor, and defender James Watson, to join other fresh newcomers Aajay Cunningham and Andrew Ridden.
The White Ribbon Cup supports a campaign to raise awareness of men's violence against women, and is a new competition in the ASB Premiership season for clubs not involved in OFC Champions League.
The six teams - Hawkes Bay United, Waikato and Manawatu in the northern conference, and Canterbury United, Otago United and Wellington in the Southern group - will play two games each.
The two conference winners will meet in the final on April 1.
Canterbury coach Keith Braithwaite believes the cup will help keep his squad focused as the business end of the season looms into view.
For Canterbury, the first of two encounters with its local rival in the space of the next eight days is a crucial step towards bridging the gap to the two Auckland teams, who are busy on O-League duty this weekend.
Braithwaite said Canterbury would treat each of the Otago derby matches like any other.
For Otago, the White Ribbon Cup offers United's only shot at silverware this season, after its league playoff hopes were extinguished in a six-match winless streak since it beat Canterbury 1-0 in December.
A victory for Otago over Canterbury would set up a virtual semifinal with Wellington on March 3 in Dunedin, the prize a place in the White Ribbon Cup final.
White Ribbon Cup
Christchurch, tomorrow, 2pm
Otago United: Oswaldo Rodriguez, Jude Fitzpatrick, Matt Joy, Morgan Day, Regan Coldicott, Seamus Ryder, Ant Hancock, James Govan, Harley Rodeka, Matt Brook, Jose Cantillo, Andrew Ridden, Craig Ferguson, James Watson, Aajay Cunningham.
Canterbury: Tom Batty, Mark Johnston, Nick Wortelboer, Tom Schwarz, Geoff Macintyre, Darren White, Aaron Clapham, George Slefendorfas, Russell Kamo, Daniel Glozier, Josh Smith, Julyan Collett, Cole Peverley, Ken Yamamoto, Adam Highfield, Shawn O'Brien.
