Sami Khedira did not travel to Spain with Juventus ahead of their Champions League match with Atletico Madrid after tests discovered an irregular heartbeat.
At his pre-match news conference, Juve manager Massimiliano Allegri confirmed Paulo Dybala will start Wednesday's match against Atletico but did not disclose any details on Khedira, saying the club would later issue a statement on his condition and only revealed that the midfielder had stayed in Italy to undergo tests.
Following the news conference, the club released a statement on their website confirming that an "atrial arrhythmia" had been detected.
"Sami Khedira has stayed in Turin for medical tests, from which emerged the opportunity to perform an electrophysiological study and eventual treatment of an atrial arrhythmia which appeared today [Tuesday]."
Khedira had trained as normal on Monday and Tuesday, with the former Real Madrid player posting a picture from Tuesday's session on his Twitter feed.
The 31-year-old has made 15 appearances for Juventus this season and played in their last two fixtures against Sassuolo and Frosinone.