Austin Watson on Tuesday pleaded no contest to domestic assault in Franklin, Tennessee.
The Nashville Predators forward can have the misdemeanor charge dismissed if he fulfills the terms of a judicial diversion program, The Associated Press said.
"Following today's events in Nashville, we have notified the Club and the NHLPA that the League will be initiating a full investigation into the matter, pursuant to the procedures set forth in the collective bargaining agreement, to determine the extent to which League discipline for Mr. Watson's off-ice conduct may be warranted and/or appropriate," the NHL said in a statement. "The Club understands and agrees fully with the League's view as to the extremely serious nature of the situation and has pledged its full cooperation in the process. We will refrain from making any further public comments on the matter until our investigation is complete."
Watson, 26, was arrested June 16 after an incident with his girlfriend.
"We will consult and cooperate with the NHL as an investigation is conducted into this matter, and will have no further comment until the NHL's investigation has reached its conclusion," the Predators said in a statement. "Our priority right now is surrounding Austin, Jen and their family with the care and resources they need to heal and move forward."
Watson has played 216 NHL games since he was the No. 18 pick in the 2010 NHL Draft by Nashville.