MLR was launched in 2018 and currently has nine teams, but that will be expanded to 12 for 2020, when Old Glory DC will enter the competition along with sides from Boston and Atlanta.
"The US market has long been a strategic target for us and the potential and passion for rugby will undoubtedly grow in the years to come," McKay said.
"It is important we are creative and develop opportunities beyond our own borders and we are very much looking forward to growing our relationship with the team in Washington in the years to come."
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(Reporting by Nick Said; Editing by Toby Davis)
