The team announced Ballard will be sidelined for up to five weeks after fracturing a bone in his hand during Monday night's 5-1 loss at Columbus.
Ballard, who played all 82 games as a rookie last season for Phoenix, blocked a shot with his right hand in the first period and missed the rest of the game.
He returned to Phoenix to be examined by team doctors and the fracture was detected. It is not yet known if Ballard will need surgery.
Yandle had two assists and four penalty minutes in two games with the Rampage this season after being one of Phoenix's final preseason cuts.
The 20-year-old Yandle, a Boston native, is in his first professional season after leading all Canadian Hockey League defensemen in scoring and being named CHL Defenseman of the Year last season.