Juan Carlos I "is showing a lack of ethics and respect for many people in this country that are suffering a lot," Cayo Lara Moya, federal coordinator of the United Left political coalition, told reporters after the monarch had successful hip-replacement surgery Saturday following a fall during an elephant-hunting trip in Botswana, a country in southern Africa.
The 74-year-old king, hunting in the Kalahari Desert, tripped on stairs in the chalet where he was staying, said San Jose Hospital in Madrid, where Juan Carlos had his operation.
Sanctioned elephant hunting is allowed to cull herd numbers.
Juan Carlos' cost of shooting a single elephant was likely $9,000 to $26,000 on top of travel expenses, Spanish Federation of Hunting President Andres Gutierrez Lara told British newspaper The Daily Telegraph.
The king is honorary president of the Spanish branch of the World Wildlife Fund for Nature.
"King Juan Carlos has lost touch with reality. Or at least so it seems," wrote El Pais columnist Antoni Gutierrez-Rubi, who called the trip "totally inadequate, improper and unjustified."
"But the key question is," he asked, "What if he had not fallen? Well, we would not know because the royal family does not report the king's private activities."
The palace declined to disclose how the trip was funded.
It came several weeks after the king publicly expressed worry over Spain's recessionary economy, which has close to 23 percent unemployment and a record 4.75 million unemployed.
He called on all Spaniards to tighten their belts to weather the economic crisis.
"One of the consequences of the crisis, youth unemployment, gives me sleepless nights," the king told a group of students in Barcelona last month.
"Talk of tightening every belt [except for those] who is not deprived of their safaris in Botswana," political blogger Koldo Aldai wrote on Facebook.
News of the accident broke on a day many Spaniards marked the 81st anniversary of the birth of the Second Spanish Republic.
Last week Juan Carlos' 13-year-old grandson, Felipe Juan Froilan, accidentally shot himself in the foot with a shotgun he was not licensed to use during target practice at a family estate north of Madrid.
He is still recovering in a Madrid clinic, near where his grandfather is hospitalized.
Juan Carlos' son-in-law, Duke Inaki Urdangarin of Palma, Majorca, is separately accused of diverting nearly $8 million in public funds for his own benefit through his non-profit institute for work that was never done or dramatically over-budgeted.
When asked by a judge during a February hearing how his 3- and 4-year-old children became partners in the institute, Urdangarin said he loved the idea of a family business, Spain Review reported.
In 1956 Juan Carlos, then 18, accidentally shot and killed his 14-year-old brother Alfonso while handling a gun while on vacation in Estoril, Portugal.
The king has had eight operations since the 1980s, three of them following accidents while practicing sports.
Queen Sofia, who disapproves of hunting, is in Greece for the Orthodox Church Easter.