The former Arsenal stopper was due to join Serie A side Cagliari, but the medical was halted when the potentially fatal complication was noticed.
Cagliari’s president, Tommaso Giulini, explained why in an interview with Tuttosport.
“Unfortunately,” he said. “There was a marked apical hypertrophic cardiomyopathy when the player was subjected to cardiac magnetic resonance imaging.
“It is a dangerous heart problem that, without precautions, can cause sudden death.”
The 37-year-old called time on a 19-year career, while Cagliari will continue to look to bring in a goalkeeper before the transfer deadline.