The controversial A1073 Spalding to Eye bypass could be subject to a £9 million overspend.
Land and compensation claims, along with an embankment problem, mean figures could soar past the original £80.3 million budget, it has been revealed.
The project attracted controversy when a former Conservative leader of Lincolnshire County Council, Jim Speechley, from Crowland, was jailed in 2004 for trying to influence the route of the multi-million-pound bypass.
He was found guilty by a jury at Sheffield Crown Court of misconduct in public office.
A Lincolnshire County Council Executive document states: "It has been reported that in relation to the projected overspend for the A1073, there have been a number of additional land and compensation claims, which were in addition to the original budget.
"The projected overspend is now likely to be around £9 million.
"This project will be considered by the value for money committee again at a later date.
"The Executive has been assured that officers would be undertaking robust negotiations in order to recover these additional costs."
Paul Coathup, assistant director of highways and transportation at Lincolnshire County Council, added: "Unfortunately, we are not able to discuss the land compensation claims, or strenuous efforts being made to recover the costs of the embankment failures, because legal proceedings are still active."
The county council received £69.8 million of Government money towards the cost of the 14-mile bypass, which replaced the narrow, twisting route between Spalding and Peterborough.
The authority paid the remaining £10.5 million.
Labour leader at Lincolnshire County Council, and value for money scrutiny committee chairman, Robert Parker, said because the opening of the road was delayed by a year due to land problems, the scheme was always going to bust the budget.
"The road scheme was supposed to open on a certain day but then there was severe land slippage which had not been foreseen," Mr Parker said.
"The argument is whether it should have been foreseen.
"There should have been better research and action taken, whether by the county council or the agents the authority used. That is the key issue here.
"That delayed the opening of the road by the best part of a year.
"Ultimately that makes a huge difference with the eventual cost of the project.
"I understand the matter will come to the value for money scrutiny committee halfway through 2013.
"We will know then exactly how much overspend there has been."
The council says £9 million is the worst case scenario and hopes to bring down the figure.
It is likely that the claims being made relate to disputes over Compulsory Purchase Orders – a legal function that allows certain bodies which need to obtain land or property to do so without the consent of the owner.