The German sprinter posted a photo of himself from a hospital on his Facebook page but declined to go into specifics of what issue required surgical intervention.
"I am currently in the cardiology of the Brussels University hospital. When I was in Calpe with the team in December and we had medical check, I was told that something is wrong.
"Well everything half as wild.. last night the plane went to Brussels. This morning at 12:00 I had the surgery. After about 2:30 h everyone was done. What it was exactly at heart can and I don't want to say."
The 23-year-old won two stages of the Tour of Austria with Team Voralberg in 2019 and won the Kampioenschap van Vlaanderen while racing as a trainee with Deceuninck-QuickStep after signing a two-year contract with the team.
He did not say when he would return to training.
A photo posted by @janniksteimle96 on Jan 7, 2020 at 2:58am PST