Panathinaikos say defender Juankar was “taken to hospital for checks” after being hit by a firecracker in the course of the membership’s Greek Superleague match at Olympiakos on Sunday.
The Spanish substitute collapsed on the sting of the sector after being struck whereas warming up earlier than being carried off on a stretcher.
The match was referred to as off afterwards with the rating 1-1 after 50 minutes.
Panathinaikos say the results of the sport might be “determined within the courts”.
Juankar, 33, who performs primarily at left-back, has made 109 appearances for the Greens since signing from Malaga in 2020.
The Athens derby, known as the derby of the everlasting enemies, has been marred by ugly scenes up to now, with a 2019 match between the rivals deserted when followers fought with riot police.
Olympiakos host Premier League aspect West Ham in a Europa League group stage match on Thursday.
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