Construction giant Leighton Holdings has written off its $63 million investment in troubled Brisbane toll road operator BrisConnections.

BrisConnections, the owner of Brisbane's airport link toll road, is in talks with its lenders about a potential restructure after saying its debt may outweigh the value of the company.

Leighton on Wednesday said it would impair its $63 million deferred equity commitment to BrisConnections.

The write-off will have no impact on Leighton's previously advised underlying net profit forecast of $400 million to $450 million for the year to December 31, the company said in a statement on Wednesday.

The impairment will be offset by the $115 million gain on the recent sale of the Thiess Waste Management business, Leighton said.

AAP