Mercer will not be available for the start of training camp due to his ongoing contract dispute, Amanda Stein of the Devils' official site reports Wednesday.
Mercer and the Devils are reportedly close to a new deal but until the restricted free agent is signed, he won't be able to get onto the ice with his teammates. Once he puts pen to paper, the 22-year-old natural center should be in the mix for a top-six role, though he could face a strong challenge from Tomas Tatar for a second-line spot.