Frankie Muniz, the 26-year-old former star of the U.S. sitcom \"Malcolm in the Middle,\" suffered a mini-stroke last week, TMZ reported Tuesday. Doctors are still trying to determine what caused the medical condition, the celebrity news website said. Friends took the actor, musician and occasional race-car driver to an Arizona hospital Friday after he had trouble speaking and understanding words, TMZ said. He was told he suffered a mini-stroke and tests are being conducted to find out why. Muniz\'s film credits include \"Big Fat Liar,\" \"Stuck on You\" and \"Agent Cody Banks.\"