Walker (undisclosed) didn't practice Monday, Barry Jackson of the Miami Herald reports.
The Dolphins signed a pair of new inside linebackers in Walker and Jordyn Brooks (undisclosed) in early March, but each offseason acquisition is now dealing with an injury. Head coach Mike McDaniel told reporters Monday that he expects Walker to return "sooner than later," so the 28-year-old's injury is likely minor. However, it's definitely something to monitor as the preseason continues.