"We know that he does have an injury but we don't know to what extent," Giants coach Tom Coughlin said.
Asked if Nicks would play Monday night against St. Louis, Coughlin responded, "I don't know the answer to that. They are checking that out now."
ESPN reported that Nicks had an MRI, which did not show anything serious.
Tight end Travis Beckum didn't play in the opener due to a tight hamstring.
"I am going to see how it feels," he said. "As hard as it is to not play, you still have to look into the best interest of my hamstring and try to get back as soon as possible and help this team win. I don't want to try to push it a couple more days when I can be resting and come back even stronger."
Coughlin also said he wasn't sure if defensive end Justin Tuck would practice this week. He sat out the season opener due to a lingering neck injury he suffered in a preseason game against the Jets on August 29.
"The plan is to progress," Coughlin said of Tuck. "If the doctor gives him the okay, then he goes and practices. I would like to see him practice."