"She's not in any rush to get out until doctors have exhausted all their list of possible tests," McGrath said. "I don't think she's going to get out (Monday). I'm not sure if it will happen (Tuesday) either."
McGrath declined to go into further detail about what might be ailing Barbara Bush, only saying "it's not life threatening."
Former President George H.W. Bush drove his 84-year-old wife to Methodist Hospital in Houston, where the couple lives, on Saturday morning. The former first lady hadn't been feeling well for about a week.
Barbara Bush had heart surgery in March 2009 for a severe narrowing of the main heart valve. She also was hospitalized in November 2008, when she underwent surgery for a perforated ulcer.