Locker suffered a Lisfranc injury in his right foot when he slowed down on an option run for an eight-yard gain during Sunday's 29-27 defeat to the previously winless Jacksonville Jaguars.
The 25-year-old was told that he would miss the remaining seven games of the season after undergoing a scan on the injury yesterday, and Munchak made no attempt to hide his disappointment at the news.
"We don't know as far as when and if he'll need surgery and how they will handle that going forward. But he won't play the rest of the year," Munchak told reporters.
"It's very disappointing, it's hard on the team. To lose him now is a huge blow."
Ryan Fitzpatrick, who was the replacement quarterback in Sunday's game, threw one touchdown pass and four interceptions in his two matches filling in for another injury to Locker earlier this season.