Toby Morland has been signed as cover for O'Leary on a five-month contract.
Morland, who had a spell with Otago before moving to the Chiefs, featured in the 2009 Super 14 final.
Originally from Oamaru in North Otago, he will join up with the Munster squad on July 1.
The 26-year-old moved from Otago to the Chiefs on the back of some strong performances in the Air New Zealand Cup.
He made his Super 14 debut with the Highlanders in 2004.
Speaking to the Otago Daily Times, he said: "I wanted a short-term contract for a start. I will then carry on or look elsewhere.
"I'm keen to get experience overseas and live a different lifestyle."
The talented half-back played in the recent Super 14 decider against the Bulls, dubbing it 'an awesome experience.'
"I had a dream run with the Chiegs. They were some of the biggest games of my career.
"I've had a bit of everything this year. It's been an exciting new life for me. Being in a winning team helped.
"I enjoyed the attitude of the coaching staff, who gave me positive reinforcement."