One of Barack Obama's longstanding mentors and oldest friends told the Times of London on Tuesday that he believes Bill Clinton will be a complicating factor for the new president and that his list of foreign donors could prove embarrassing.

Abner Mikva, a former federal judge who was Clinton's White House counsel -- and an early supporter and close friend of Obama -- told the Times that the choice of Hillary Clinton as secretary of state worried him because of her husband.

"I worry about the difficulty not that she brings, but that her husband brings," he said over breakfast at the University of Chicago, where he recently retired as a law professor. "His entire career since leaving the White House has involved foreign contacts, foreign speeches and foreign contributions," Mikva, also a former congressman, said. He is not a member of Obama's transition team.

"I don't know how you separate her activities from his -- how you vet those. As far as I'm concerned they will all have to be made public. I think that will be very embarrassing to President Clinton and to the donors."

One of the main stumbling blocks to Hillary Clinton's nomination as Obama's secretary of state -- which will be announced formally next week -- was her husband's financial ties to foreign governments, and the list of donors to his philanthropic foundation and presidential library.

After negotiations between both camps last week, former President Clinton agreed to hand over the names of more than 200,000 donors to the Obama White House transition team, and to have future foreign speeches and engagements vetted so as to avoid any potential conflicts of interest with his wife.

"I'm not saying there is anything illegal," Mikva told the Times. "But it causes complications trying to make clear that what they do in private has nothing to do with our foreign policy."

Click here for the story from the Times of London.