“I was in contact with his wife Claudine last night,” he told Belgian broadcaster Sporza.
“According to her, it is, all in all, ok. Today, new tests are planned.”
Merckx is one of the most decorated cyclists of all time, having won five Tour de France and five Giro d’Italia titles, as well as a solitary Vuelta a Espana to complete a career Triple Crown of Cycling, something only seven men in history have managed.
He also won three World Championships and 19 Monument races, including a record seven Milan-San Remo titles.
The news of Merckx’s hospital admission comes just a few weeks after Tour de France star Raymond Poulidor, a former competitor of the Belgian who won seven TdF stages and a Vuelta title, was taken ill in central France.