The condition of Spain international Antonio Puerta has deteriorated after he suffered a heart attack in Sevilla's 4-1 win against Getafe on Saturday.
Puerta, 22, collapsed in the first-half and medics prevented him from swallowing his tongue.
But he collapsed again after going off and was given cardiac resuscitation before going to hospital.
"The player remains in the hospital in a very critical state and his progress is unfavourable," said doctors.
Puerta collapsed after jogging back towards his own goal 35 minutes into the opening league game of the season at the Sanchez Pizjuan on Saturday.
Team mates and medical staff rushed to his side and were seen preventing him from swallowing his tongue as he lost consciousness.
He was able to walk from the pitch but doctors said that he collapsed again in the changing rooms and had to be given cardiac resuscitation before being taken to hospital.
AC Milan, Sevilla's opponents in Friday's European Super Cup, issued a statement on Sunday wishing the player a speedy recovery.
Team-mate Ivica Dragutinovic was first to Puerta's aid and midfielder Renato said: "We were very frightened, but the doctors knew what they were doing.
"It was difficult to continue playing. This victory is dedicated to Puerta."
Sevilla coach Juande Ramos was in no mood to talk about his side's victory after the match.
"I don't have the mind to speak now. The reason I am here is because we are all professionals, but I have no desire to talk of the game or anything," Ramos said.
"I would like to see the player. The game does not have any importance compared with the health of a player."
Puerta, 22, collapsed in the first-half and medics prevented him from swallowing his tongue.
But he collapsed again after going off and was given cardiac resuscitation before going to hospital.
"The player remains in the hospital in a very critical state and his progress is unfavourable," said doctors.
Puerta collapsed after jogging back towards his own goal 35 minutes into the opening league game of the season at the Sanchez Pizjuan on Saturday.
Team mates and medical staff rushed to his side and were seen preventing him from swallowing his tongue as he lost consciousness.
He was able to walk from the pitch but doctors said that he collapsed again in the changing rooms and had to be given cardiac resuscitation before being taken to hospital.
AC Milan, Sevilla's opponents in Friday's European Super Cup, issued a statement on Sunday wishing the player a speedy recovery.
Team-mate Ivica Dragutinovic was first to Puerta's aid and midfielder Renato said: "We were very frightened, but the doctors knew what they were doing.
"It was difficult to continue playing. This victory is dedicated to Puerta."
Sevilla coach Juande Ramos was in no mood to talk about his side's victory after the match.
"I don't have the mind to speak now. The reason I am here is because we are all professionals, but I have no desire to talk of the game or anything," Ramos said.
"I would like to see the player. The game does not have any importance compared with the health of a player."