Former Portugal and Benfica great Eusebio was taken to hospital on Saturday in the Polish city of Poznan where he has been watching matches at Euro 2012, the Portuguese Football Federation (FPF) said in a statement.
"Portugal's football ambassador Eusebio felt indisposed on Saturday when he was at the hotel with the national team in Opalenica," the FPF said in a statement. "After a first observation and contacting his doctor in Lisbon, he went to a hospital in Poznan as a precaution where he is being examined".
Eusebio, who turned 70 in January, has been admitted to hospital three times since December. He has been suffering from hypertension and his doctors have said he must have regular examinations.
He travelled with the national team to Poland and was in the stands for the quarter-final win over the Czech Republic, cheering alongside former Portugal captain Luis Figo. Portugal face Spain in the semi-finals on Wednesday.
Nicknamed the 'black panther', Eusebio grabbed international headlines during the 1966 World Cup in England when Portugal finished third.