 On October 17, after playing in four games for the Senators, it was announced that Tkachuk had a torn ligament in his leg and was set to be out for a month to recover.Tkachuk eventually returned to the Senators line-up on November 8, 2018, for a game against the Vegas Golden Knights.On March 28, 2019, in a game against the Florida Panthers, Tkachuk tied the Senators' franchise record for most shots on goal in a game with 12.