Tenerife say Jesus De Migue's condition has 'worsened' after the striker suffered serious injuries during a Spanish second division match.
The 30-year-old suffered head and chest injuries during Monday's home game against Andorra, after a heavy collision with goalkeeper Jesus Owono, who was sent off for his challenge.
Spanish media, including Marca, external, reported De Miguel had a cardiac arrest in an ambulance and was resuscitated by paramedics on the way to hospital.
An initial statement from Tenerife on Monday said De Miguel was "stable" in hospital, despite the "severity of his condition".
However, a further update from the club in the early hours of Tuesday morning said the striker's "medical condition has worsened neurologically" and there would be "more information in the coming hours".
Tenerife and Andorra were drawing 2-2 seven minutes into stoppage time when the incident occurred.
Owono had run towards the centre circle to clear a long ball when his knee appeared to collide with De Miguel.
Source: BBC Sport