Placido Domingo says he expects to feel "much better soon" after treatment for a blockage in his lung which forced him to cancel a number of concerts in Madrid.
"I will be feeling much better soon. Thank you all from the bottom of my heart," the Spanish opera star told his fans in a message on Facebook.
Domingo, 72, was admitted to hospital on Monday.
"He is being successfully treated for a pulmonary embolism," a blockage of an artery of the lungs, and is expected to make a full recovery, his agent Nancy Seltzer said in a statement.
She said the embolism was caused by deep vein thrombosis - a condition in which a clot forms in a deep vein, often in a leg.
"He will be forced to rest for three to four weeks. His exact return to his performing engagements remains subject to how fast he can heal and regain his characteristic strength."
The singer had to cancel five performances in "Il Postino", due to begin at the Teatro Real in Madrid on 17 July.
He also bowed out of a concert he was due to conduct in Plaza Mayor square in Madrid on 21 July.