Jun Byung-hun, the senior presidential secretary for political affairs, offered to resign Thursday over a burgeoning graft scandal involving his two former aides.
In a meeting with reporters, Jun repeated his denial of any involvement in the scandal and said he is ready to face a prosecutorial probe.
"I feel very frustrated that I have caused trouble to the president though I have done my best to serve him in the short period of time," he said.
"I am once again sorry for the aberrant acts that my former aides had carried out... I will explain my position to the prosecution any time," he added.
His offer to resign came a day after the prosecution said it would "inevitably" question Jun over the scandal.
The scandal has been posing a tricky dilemma for President Moon Jae-in, as it could undercut the government's anti-corruption crusade and reform drive.
Despite Jun's denial, concerns are rising that he could become a political liability for the young administration and embolden opposition parties to escalate their offensive.