The 72-year-old, popularly known for his "Three Tenors" performances with José Carreras and the late Luciano Pavarotti, was admitted to hospital in the Spanish capital and treated for a pulmonary embolism.
"I am lucky to be feeling very well. What hurts me the most is not to be able to sing in front of Madrid audiences," said Domingo, who was forced to cancel a string of performances.
"The doctor asked me to rest between three and four weeks," he told reporters at Madrid's opera house.
Domingo's doctor said that the star was expected to make a full recovery and resume singing.
"He will be able to recover completely and will not be constrained in his artistic and professional activities," said Carlos Gonzalez, who appeared with the tenor.
Domingo's agent had earlier in the week said that the embolism was caused by deep vein thrombosis — a condition in which a clot forms in a deep vein, often in a leg.
The Grammy-winning singer had to cancel five performances in Daniel Catan's opera "Il Postino", due to begin at the Teatro Real in Madrid .
He also bowed out of a concert he was due to conduct on Madrid's Plaza Mayor square on , the agent said.
he said there was a "large probability" that he would have to cancel performances at the Salzburg festival on , 10th, and 13th.
Born in Madrid, Domingo moved to Mexico as a child with his parents, who ran a company that performed zarzuela, the traditional Spanish operetta form.
His repertoire encompasses 140 stage roles — a number unmatched by any other celebrated tenor in history.