Caisse president and CEO Richard Guay resigned Monday for personal reasons. Only five months after he was named to the job, the head of Quebec's Caisse de dépôt et placement is quitting.

Richard Guay, 47, stepped down Monday as the president and CEO of the Caisse de Depot — the country's biggest pension fund manager.

In a statement, Caisse chairperson Pierre Brunet said Guay stepped down for personal reasons.

"The Board of Directors has accepted his resignation. It understands Mr. Guay's decision and has thanked him for his contribution to the Caisse's management," said Brunet.

Guay took over the top two posts at the Caisse in September after serving as interim president and CEO since May. He went on medical leave in mid-November, and had been expected to return to work Monday.

His resignation as president and CEO will take effect on Wednesday.

Brunet said Guay will continue to work for the Caisse as the strategic adviser to the next president and CEO. He will give counsel on investment policy and asset allocation.

"The Caisse is pleased that it can continue to rely on his expertise and in-depth knowledge of the organization and financial instruments," said Brunet.

The Caisse's board is recommending the Quebec government approve the nomination of Fernand Perreault as the interim president for the next six months. Perreault has been filling in for Guay in his absence. He was most recently vice president of the Caisse's real estate division.