Donald has replaced an injured Colin Slade in the All Blacks squad, joining fellow call-up Aaron Cruden, who took over from a stricken Dan Carter.
Cruden or versatile half-back Piri Weepu are expected to wear the number 10 shirt against semi-final opponents Australia next Sunday, but Donald could also feature in the selection mix.
"I was fairly surprised," said Donald, who will link up with Bath following the World Cup after agreeing terms earlier this year.
"Obviously, I never gave up the dream, but I was fairly surprised considering what has happened.
"I have had a good month off, and like everyone else I have enjoyed watching the World Cup. Obviously I watched it thinking 'I would love to be a part of it,' and now that opportunity potentially is here."
Donald was fishing for whitebait on the Waikato River in New Zealand's North Island when he was alerted to his World Cup summons.
"I think Ted (All Blacks coach Graham Henry) had missed me a couple of times, and then I finally got a call from 'Milsy' (Mils Muliaina) and he said 'start answering your phone, you idiot,' so that was sort of the message I needed.
"I was keeping fit and just waiting. My chance has come now, so that is all I am worried about.
"I've had a good break, a good month away, and I have just been enjoying watching the World Cup. Now, I've been given a crack and an opportunity here, which I am extremely excited about being a part of.
"Fitness-wise, I am pretty confident, very confident."
All Blacks assistant coach Wayne Smith, meanwhile, is taking little notice of Australia fly-half Quade Cooper's erratic performance during the Wallabies' quarter-final win against South Africa in Wellington three days ago.
Despite playmaker Cooper making several errors, Australia prevailed, posting an 11-9 victory that booked a semi-final appointment with New Zealand at Eden Park.
"I can only talk about experiences that we've had with them, and he (Cooper) has played pretty well against us," former Northampton boss Smith said.
"He is mercurial, he is dangerous. If he has a real good day then you are in trouble, so we've got a lot of respect for him.
"People probably say the same thing about any player who has a bad trot.
"We had an experience with Zac Guildford (All Blacks wing) for example, who had a poor game before the World Cup, got a chance in the World Cup and then had a blinder.
"Quality players come right pretty quickly."
Smith insists it is business as usual ahead of New Zealand's biggest game in the tournament, despite the injury disruption of losing Slade and Muliaina.
"Any time you get to this stage in any tournament, whether it be Super Rugby, Premiership, Heineken Cup, World Cup, it is about will. It is about the strength of your will," he added.
"Tournaments throw up all sorts of things at you - injuries, selection - and you cannot control any of that, and it's the same for the other team.
"It is not who you've got in the team, it is what you've got inside you that counts at this point, and that is what will win it.
"We've got huge respect for them (Australia), and I am sure they've got great respect for us.
"We've played each other often over the last few years. We know them well, they know us well. We know it's going to be a massive encounter."
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