Daley was taken to Northwestern Memorial Hospital after experiencing stroke-like symptoms Friday while on a flight to Chicago from Arizona.
The 71-year-old Daley was undergoing tests this weekend after appearing disoriented on the private plane, spokesman Rick Jascula said. He was able to walk off the plane at Midway Airport, where he was met by firefighters and an ambulance.
The newspaper's source downplayed the likelihood of a stroke; however Daley remained at Northwestern overnight undergoing tests.
The Sun-Times said Daley has had similar scares in the past. Friday's attack came on the same day Daley's nephew, Richard Vanecko, pleaded guilt to involuntary manslaughter in the 2004 death of David Koschman during a fight.