The team added Cory Sullivan to the active roster but will need another pitcher -- likely Triple-A Buffalo's Nelson Figueroa or Jon Niese -- to take Nieve's spot in the rotation on Saturday and beyond.
Manager Jerry Manuel said that he would leave that decision up to the people who have seen the pair pitch often.
A team source indicated that Niese would be the choice.
Before sustaining the injury, Nieve was 3-3 with a 2.95 ERA this season in seven starts.
"It's tough to see him going down," ace Johan Santana said. "Especially in the situation where we are, when we need him the most, because he was doing a great job for us. We still have to find ways to keep it up and keep going. There's not much you can do."
The 27-year-old is the latest entry to a seemingly endless list of Mets who are injured. The team has nine players, including four pitchers, on the disabled list.
"It's been crazy," Santana added. "We try to do everything the right way, and things don't go the right way for us. We're getting people hurt and going down like that."
Mark Selig is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.