"They'll let it calm down, and then at some point he will have surgery," Spagnuolo told the St. Louis Post-Dispatch. "He was having a terrific game. Donnie's a quality guy and a character guy, and we'll miss him."
Avery, a second-round draft pick out of Houston in 2008, had 53 receptions as a rookie and started 28 games in his first two seasons. He caught two passes for 48 yards Thursday before being injured.
"Probably between Danny (Amendola) and Mardy Gilyard, and a couple of the guys we could flip over there (such as) Keenan Burton," Spagnuolo told the Post-Dispatch. "We're going to wait a little bit before we declare any of that, but certainly somebody's going to have to step up there."
The team might look beyond the roster for help.
"We're always looking for players; (general manager Billy Devaney) has been on top of that and will continue to do it," Spagnuolo said. "But I can't go on a ghost body right now, so I'm just going to go with the players we have here."
The Associated Press contributed to this report.