The Argentine was withdrawn at halftime in the 2-2 draw at Parc des Princes on Tuesday after suffering a hamstring injury shortly after putting Barcelona in front on the night.
He has since undergone tests on the injury, and the club has confirmed he has a problem with his right femoral bicep, ruling him out of Saturday's Liga match with Mallorca, leaving his participation against PSG in doubt.
"Tests have confirmed that Leo Messi has a muscle injury in the femoral bicep of his right leg," a club statement read.
"He is out for the Liga match on Saturday, and his rate of recovery will determine his availability for subsequent commitments."
The player himself moved to assure fans that the injury was not serious, and wished teammate Javier Mascherano a speedy recovery from his own knee problem.
"I will return soon, thankfully it was not so serious," he said on his Facebook page.
"We feel very sorry for Masche [Mascherano], and wish him strength so that he can return quickly."