The French waste and water group has long sought to exit Transdev and has an option to sell its 30 percent stake at the year end under a 2016 agreement with the CDC.
"We've got two options we are undoubtedly going to make a decision on towards the end of summer," CDC head Lombard told Reuters in an interview.
"Either we buy Veolia's stake or (we reach) a deal with either a financial or industrial partner to buy the 30 percent," he added, speaking on the sidelines of an economic conference in Aix-en-Provence, southern France.
Apart from Transdev, Lombard said that he did not see a pressing need to make other adjustments to the CDC's considerable portfolio of French corporate stakes after a review of its holdings since he joined last November.
He said he saw no pressure for French ski operator La Compagnie des Alpes, in which the CDC owns a 39.5 percent stake, to form a partnership with another company to pursue its development.
In December, the company, which also owns leisure parks, said it was confident of making progress in selling a stake to potential investors including China's Fosun as it seeks to expand abroad into high-growth markets.
"La Compagnie des Alpes is doing well. If management has plans, we'll have a look, but they are under no obligation to move if everything is going well," he said.
Lombard said he was also watching from a distance the government's plans to privatise Paris airport operator ADP.
Though his predecessor had said last year that the CDC could be interested in buying a stake in ADP, Lombard said that there was not an obvious logic in a public body like the CDC participating in a privatisation.
CDC currently has a 41 percent stake in insurer CNP Assurances, which the French press suggested in January could be combined with the state-controlled postal service's bank.
Lombard said that work was still under way and that the government had not taken a decision yet. "There is no urgency... It's still possible that nothing happens."
(Reporting by Leigh Thomas; Editing by Ingrid Melander and Stephen Powell)
By Leigh Thomas