The 27-year-old could now miss the start of the Bhoys' Champions League campaign, after being called up by Fernando Santos, despite an existing back problem.
Samaras came on as a half-time substitute with his side trailing 1-0, a deficit which was overturned thanks to the Celtic striker's contribution.
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His lawyer, Gregory Ionnidis told BBC Sport: "He needs an MRI scan and I fear the injury is extremely serious.
"Sammy shouldn't be playing in the first place with his bad back."Sammy needs to get back to Glasgow asap," Ionnidis added on Twitter
"He is now in terrible pain and his left arm is injured. Why did they have to use him?"
Celtic did receive some good news about Dylan McGeouch though, ahead of their Champions League Group G game at home to Benfica on September 19.
The 19-year-old suffered a broken jaw in a pre-season friendly against Real Madrid in Philadelphia but was told he can resume training with the first-team squad earlier than expected.
"Being out for a few weeks has been frustrating as everything has been fine with my legs, but it's been a waiting game with my jaw," he told the club's official website.
"So hopefully I can get back into training this week and push on and get back into the squad as soon as possible and see how it goes."