Spach tore his right anterior cruciate ligament while blocking in the second half of Saturday night's 33-13 victory over the Carolina Panthers.
He was signed as a free agent on Oct. 28 to shore up the injury-depleted position and became a starter against the San Francisco 49ers on Nov. 10. His blocking helped the team's improved running game, and he had a game-clinching 23-yard catch on a third-and-16 situation late in Arizona's 30-24 wild-card victory over the Atlanta Falcons.
Meanwhile, it was uncertain if Pro Bowl receiver Anquan Boldin, who sat out against the Panthers with a strained left hamstring, would play in Sunday's NFC Championship Game against the Philadelphia Eagles.
Boldin tested the injury just before kickoff at Carolina and decided he wasn't ready to go. He said afterward that if the injury continued to improve, he liked his chances of playing in the NFC title game.
"We're a week further along in the process of that hamstring getting better, so hopefully he'll be able to do something this week," coach Ken Whisenhunt said, "but we'll see as the work progresses."
Spach had appeared in the first two games of the season for the New England Patriots before being released Sept. 15.
Spach "has done a good job for us in the running game, but it's not going to change our scheme," Whisenhunt said Monday. "I think we're very comfortable with Ben and Leonard in doing what we've been doing. They're healthier than they were at times this year when we've struggled so it shouldn't be a big issue."
Whisenhunt said the team would look to sign another tight end. A leading candidate would be 10-year NFL veteran Jerame Tuman, who was released by the Cardinals on Dec. 24.