In a statement issued Friday in Washington, Jackson said he will testify if necessary.
Blagojevich faces federal charges including allegations he schemed to sell a U.S. Senate seat once filled by President Barack Obama.
According to a criminal complaint, Blagojevich tried to shop the seat to Jackson. The Democrat's supporters allegedly were willing to raise $1.5 million for Blagojevich if he him.
Jackson said if he testifies he will tell the truth, saying he did nothing wrong and ``never authorized or engaged in any scheme related to the then-vacant Senate seat.''