The champion horse is currently coughing and his blood profile is not normal, his trainer, Bill Mott, told ABC News. The Preakness Stakes, the second round of the Triple Crown, is set for May 18.
Country House was determined the Derby winner when a controversial decision disqualified Maximum Security, the first horse to cross the finish line, after a review found Maximum Security veered out of his path on the final turn.
An appeal filed by Maximum Security's owners was denied by the Kentucky Horse Racing Commission.
Maximum Security will not race in the Preakness Stakes either, his co-owner, Gary West, told the Associated Press on Monday.
There is "really no need" for Maximum Security to run the Preakness, West told the AP, since he will not have a chance to go for the Triple Crown.
Additional details on Country House's health were not immediately available.
ABC News' Courtney Condron contributed to this report.