"Jahmir Hyka, Gamal Hamza, Peter van der Heyden and Niko Bungert were infected," the German club said in a statement on their official website.

"Training was cancelled to reduce the risk of infection ahead of the league match against VFL Bochum."

Hamza is unlikely to feature in Saturday's Bundesliga game away to Bochum.

The 27-year-old, who joined Mainz in the close season after his contract with Zamalek expired, is yet to make his league debut.

He was recently criticized by coach Thomas Tuchel for not showing enough commitment in training.