The defect was discovered after the French international passed a medical on Thursday and put pen to paper on a five-year contract to complete his transfer from top-flight rivals Nice.
Nothing showed up at his medical but the problem emerged later when doctors took a closer look at scans.
"More tests will be performed on Monday to give clear answers to Loic," Marseille doctor Christophe Baudot told reporters on Friday. "He will not play for as long as there are any doubts."
Remy, who has two international caps, cannot now make his Marseille debut at home to Lorient on Saturday.
"The news we've had since (Thursday's scans) is reassuring but we have taken this decision because the most important thing for us is not to take risks with our players' health," said president Jean-Claude Dassier.
WORRIED REMY
The incident was reminiscent of June 2008 when former France defender Lilian Thuram was unable to sign for Paris Saint-Germain and had to end his career after having a heart condition diagnosed during a medical.
Last year, forward Steve Savidan's move from Caen to Monaco collapsed for the same reason and he, too, had to hang up his boots.
"It's a nuisance but the most important thing is my health," said Remy who joined Marseille for an undisclosed fee.
"It's a pity that tests did not show that earlier. I'm a bit worried but not to the point I fear I might have to end my career."
Remy started out at Olympique Lyon and joined Racing Lens in 2007 before moving to Nice the following year. He scored 14 league goals last season.
Marseille are third from bottom and without a point after losing their first two matches of the season.
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