Zeitler, the team's starting right guard, was injured during Wednesday's practice and did not participate in Thursday's session.
"He is going to be OK, but he is going to be down for a little while," Browns head coach Hue Jackson told reporters. "It is a calf. It is unfortunate, but we will get him back. We will be back and ready to go hopefully in the next couple of weeks or so. Those things do happen in training camp."
Zeitler, who was signed to a five-year, $60 million contract in March 2017, started all 16 games a year ago in his first season with the Browns.
A first-round pick of Cincinnati in the 2012 NFL Draft, the 6-foot-4, 315-pound Zeitler spent his first five seasons with the Bengals, starting 87 of 88 games, including all 16 in 2015 and 2016.