Sonny Colbrelli suffered an unstable arrhythmia and doctors confirmed that he needed immediate defibrillator treatment after collapsing at the finish of the first stage of the Volta a Catalunya on Monday.

Bahrain Victorious confirmed in a medical update that doctors have not yet determined the cause of Colbrelli's irregular heartbeat and that he will undergo additional tests at the University Hospital of Girona on Wednesday.

"After the first stage of the Volta a Catalunya, our medical team confirmed that Sonny Colbrelli suffered an unstable arrhythmia requiring defibrillation.

"The cause has not yet been identified and the Italian rider will undergo further tests tomorrow at the University Hospital of Girona.

Colbrelli finished second in the first stage of the uphill sprint of San Feliu de Gixol, but collapsed just 100 meters from the finish and required urgent medical attention. After being treated locally, he was taken to the hospital by ambulance 45 minutes after the stage.

The team confirmed that Colbrelli was in stable condition when he was transported by ambulance to the University Hospital of Girona for additional treatment and thanked the medical staff on site for their help.

"The team would like to thank Borja Saenz de Cos, an emergency nurse from the Sistema d'Emergencies Mediques (Catalan Emergency Services), for her prompt assistance at the finish yesterday and for supporting the medical staff in handling the accident.

Corbrea, who was the first to be assigned to the hospital.

Colbrelli is currently recuperating in the hospital, where the team has announced that he shows no signs of cardiac decompensation. Initial tests showed positive results, but doctors aim to determine the cause of his cardiac arrhythmia in a series of follow-up tests on Wednesday.

"Sonny Colbrelli's clinical situation is good and we wish him a speedy recovery.

With Colbrelli and Jack Hague sidelined, Bahrain Victorious will remain in Volta a Catalunya with Wout Poels, Dylan Tuns, Phil Bauhaus, Santiago Buitrago, and Hermann Pernsteiner.

Cycling News spoke with Poels at the start of the second stage in Lescala and wished his teammate Colbrelli a full recovery.

"Yesterday was a strange day, especially after the course," Poels said. 'Let's hope Sonny Colbrelli makes a full recovery. The team told us everything we know in their press release."