(Video at left: Watch Sen. Grassley's interview.)
"If this hadn't come up...this would have been handled very quickly, to get a new secretary of the Treasury sworn in very quickly," Grassley said.
Grassley said, as with any nominee, he would not make up his mind on whether to support Geithner until after the hearing, which is now set for Jan. 21.
As a result, Geithner won't be able to be confirmed in time to take office next Tuesday, when Obama is sworn into office.
Democrats and Republicans on the panel are voicing support for Geithner despite revelations this week that he failed to pay $34,000 in taxes several years ago. Geithner has paid back the taxes he owed.
And, panel chairman Max Baucus, a Montana Democrat, says Geithner's confirmation is "a given."
Baucus also told reporters he believed Geithner would win approval despite questions over his taxes and a housekeeper who worked for him briefly without proper immigration papers.
Asked when he would hold a hearing on Geithner, Baucus said: "As soon as possible, but it's looking like the latest date will be Wednesday. Earlier if we can."
Asked if Geithner would ultimately be confirmed, he answered: "Yes, clearly."
Utah Republican Sen. Orrin G. Hatch calls his tax problems "a mistake that a human being can make," and Kansas Republican Pat Roberts says he'll probably vote to confirm Geithner.