The first-term Illinois treasurer, a Democrat who's locked in a contentious race for President Obama's old Senate seat with Republican Congressman Mark Kirk, told The Associated Press that he was subpoenaed by Blagojevich's defense team.
Giannoulias' name was mentioned briefly last week during Blagojevich's trial. Former Blagojevich chief of staff John Harris was heard on federal wiretaps mentioning that Giannoulias had called about Obama's old seat on behalf of someone else.
Giannoulias told the AP that he introduced a friend of Obama's to Tom Balanoff, an official with the Service Employees International Union. The friend, Valerie Jarrett, allegedly was Obama's choice to replace him in the Senate after he was elected president.
Prosecutors say Blagojevich sought favors from the White House in return for Jarrett's appointment and delivered the message through Balanoff.
Blagojevich, 53, has pleaded not guilty to charges that he schemed to get a large payoff, a high-paying job after he left office or a big campaign contribution in exchange for the Senate seat. He also has pleaded not guilty to conspiring to launch a racketeering scheme using the power of the governor's office.
If convicted, he could face up to $6 million in fines and a sentence of 415 years in prison, although he is certain to get much less time under federal guidelines.
"Tom Balanoff reached out to me to get in touch with Valerie because he didn't know how to get a hold of her, and I put the two of them together," Giannoulias said.
He said he also attended an informal meeting between Jarrett and Balanoff shortly after Obama's election but "didn't really participate in it" and doesn't remember what they talked about. He said he never talked to Obama or Blagojevich about the matter.
Last week, prosecutors at Blagojevich's trial played an FBI tape on which Harris is heard telling the governor that the Obama camp sent word that it would be "thankful and appreciative" if Valerie Jarrett were appointed to the Senate seat. Blagojevich is heard telling Harris not to meet with Giannoulias about the matter.
Jarrett, a Chicago businesswoman and former aide to Mayor Richard M. Daley, was a longtime Obama family friend.
Blagojevich had allegedly sent word through Balanoff that he would appoint Jarrett if Obama agreed to appoint him as secretary of health and human services.
Blagojevich apparently took the words "thankful and appreciative" as a sign that the Obama camp didn't want such a deal. Jarrett later withdrew her name and is now a White House adviser.
Blagojevich named former Illinois Attorney General Roland Burris to the Senate.
Giannoulias said he voluntarily talked to federal investigators about the meeting between Jarrett and Balanoff, but "they politely sent me on my way," because there was nothing noteworthy about it.
He said he doesn't expect that he will actually be called to testify. Blagojevich's attorneys also have subpoenaed Jarrett, White House chief of staff and former Illinois Congressman Rahm Emanuel, Illinois Sen. Dick Durbin and Senate Majority Leader Harry Reid.
"They subpoenaed any and everybody to try and get everyone involved from the president down to the dog catcher, so I think this shouldn't be surprising," Giannoulias said.
Even so, the subpoena gives Kirk -- who has been dogged by reports that he exaggerated his military credentials -- an opportunity to associate Giannoulias with Blagojevich and Illinois corruption.
Kirk's campaign could not immediately be reached for comment.