Sergio Agüero was taken to hospital for a cardiac exam after leaving the field early as Barcelona began life after Ronald Koeman with an uninspiring 1-1 draw at home to Alaves in La Liga on Saturday night.
Former Manchester City striker Agüero was making his first start at the Nou Camp since his summer transfer but his evening lasted just 41 minutes.
The 33-year-old Argentinian reported chest discomfort and appeared to be suffering breathing problems, although he managed to walk from the field as he was replaced by Philippe Coutinho.
A tweet from Barcelona read: “ aguerosergiokun reported chest discomfort and has been admitted to the hospital for a cardiac exam.”
With Barcelona great Xavi expected to become permanent successor to the sacked Koeman, B team coach Sergi Barjuan took control of Saturday evening’s game.
Memphis Depay put Barca ahead four minutes after half-time but the hosts were unable to fully bounce back from successive defeats to Real Madrid and Rayo Vallecano as Luis Rioja swiftly equalised.
Real Madrid reclaimed top spot – eight points ahead of ninth-placed Barca – following a 2-1 triumph at 10-man Elche.
Vinicius Junior claimed both Real goals, either side of Raul Guti being dismissed for a second bookable offence, before Pere Milla claimed the hosts' late consolation.