The 28-year-old eventer and his 11-year-old horse, Balmoral Sensation, leave for England at the end of the week to prepare for the Badminton Horse Trials in May.
A good performance there should guarantee him a top-four spot in New Zealand's six-strong equestrian team (including two reserves) for Rio.
If he makes it, it will put to bed the disappointment of missing out on the 2012 London Olympics, when his former horse, Orient Express, picked up a leg injury in the build-up.
‘‘It's been a long four years waiting for another chance,'' Johnstone yesterday told the Otago Daily Times from Hamilton, where he is now based.
Orient Express was initially forced into retirement after the leg injury, but recovered and was back competing last year.
However, the 16-year-old horse died after taking a nasty fall in the cross-country stage of a national three-day event in Taupo last May.
Balmoral Sensation has been Johnstone's horse since, and delivered a comprehensive 16-point win at the Horse of the Year Show in Hastings a fortnight ago.
Johnstone called his mount's performance ‘‘exceptional'' and said it boded well for the Badminton event on May 4-8.
‘‘I think I can put in a good performance at Badminton,'' he said.
‘‘I know the horse is good enough to do that.
‘‘The preparation so far has gone very well. Obviously, flying into England there are things that can go wrong, but at this stage it's looking pretty positive.
‘‘I'm hoping to go really well at Badminton and make it that I have to be selected.''
Johnstone said New Zealand's six-strong team was all but decided, with just the decision as to who will make the top four spots yet to be finalised after qualifiers in England and the United States.
‘‘Everyone is taking their good horses to either Badminton in England or Kentucky in America,'' Johnstone said.
‘‘It's really going to be who does the best there and who has got the horses that are nice and sound without any injury issues.''
Johnstone grew up in Outram and completed a bachelor of commerce degree at Otago University in 2008, before moving to the North Island to pursue a career in eventing.
He has had plenty of success both in New Zealand and overseas, and became the youngest winner of an eventing World Cup qualifier when he was 19.
