Transurban Group Ltd shares were down 24 cents, or 5.1 per cent, to $4.44 after one of its key shareholder, Ontario Teachers Pension Plan Board (OTPPB), sold its stake in the company.

Ontario Teachers sold its 13 per cent stake at an estimated $4.44 a share after the Australian toll-road operator rejected a $7.2 billion bid from three of its largest investors last week.

Transurban's three largest shareholders, OTPPB , Canada Pension Plan Investment Board (CPPIB), and Australian fund manager CP2 Ltd, offered $5.57 for each share but the Melbourne-based company rejected the bid.

CP2 holds a 14 per cent stake in the company and Canadian Pension holds another 14 per cent.

The three investors had their stakes diluted after they declined to buy shares in a May 12 equity raising by Transurban to help fund the acquisition of the Sydney Lane Cove Tunnel.

CP2 chief executive Peter Doherty said the company is considering the impact of OTPPB move and evaluating its options in Transurban.

Doherty said there would be mixed reactions on the exit of OTPPB.

''Those shareholders who support dilutionary equity issues ... may initially revel in another opportunity to exploit the value shift from long-term holders,'' Doherty said. ''This positive feeling may not endure as the impact of OTPPB's decision and the company's rejection is fully appreciated."

Transurban Group posted a loss of $24.58 million for the 12 months to June 30, 2009.