Portugal football legend Eusebio was given the all clear on Sunday after being taken to hospital because of high blood pressure on Saturday evening after falling ill at the team hotel, the Portuguese team doctor said.
It is the fourth time this year that the 70-year-old 1965 Ballon d'Or winner has been hospitalised.
However, the team doctor Henrique Jones told Portuguese media that Eusebio would be able to leave hospital on Monday.
"He is stable. He was joking and speaking with us. He should be up to leaving hospital tomorrow (Monday)," said Jones.
"He will stay in hospital for an extra day as a precautionary measure.
"The tests carried out today (Sunday), as well as the blood tests and x-rays, were fine."
However, Jones said that Eusebio would return to Portugal before the Euro 2012 semi-final between Portugal and defending champions Spain in Donetsk, Ukraine, on Wednesday.
"Given the status of his heart, it is preferable that he doesn't stay for the match against Spain."
Jones said Eusebio had had a number of tests, including an electrocardiogram, which revealed "some small variations".
The player, who was taken to hospital last February in Lisbon for the third time in a little over two months, has previously had neck pain and pneumonia.
Portugal defender Joao Pereira speaking from the team's base in Opalenica, Poland, said he was confident Eusebio would be absolutely fine.
"It has not had an impact on us, because we are focused on the semi-final with Spain, but I would like to say that the whole squad wishes him a speedy recovery," he said.
"He is a strong man. We know that he will recover quickly, it is because of that that we are not worried."
Eusebio, born in the former Portuguese colony of Mozambique, made his name with Benfica, with whom he won a string of domestic and international trophies including the 1962 European Cup.
"The Black Panther" was also instrumental in Portugal finishing third in the 1966 World Cup where he also top scored with nine goals.
Apart from winning the Ballon d'or he was twice the leading European goalscorer.