The 70-year-old complained of health problems while in Opalenica, where he was accompanying the Seleccao during their Euro 2012 campaign, and was consequently taken to a medical facility in Poznan.
"Right now, Eusebio is fine, he is stable," Jones told reporters. "He was laughing and talking to us. He is ready to be discharged tomorrow.
"The only reason he is not discharged today is because he has to repeat the exams he underwent. He is only staying one more day as a precaution.
"He will probably return to Portugal after this, even though that is not his wish.
"As you know, he likes to be around football as much as possible, but we will try to make sure that he returns to Lisbon in good conditions from Warsaw."
Portugal take on Spain on June 27 in the semi-finals of Euro 2012.