Mateiko was Washington's 2024 3rd-round pick (90th overall) and signed a three-year, entry-level contract on Friday worth $889,167 AAV. The 18-year-old Latvian winger is expected to return to Saint Johns (QMJHL) for his third season of junior hockey after joining the Sea Dogs from Latvia in 2022-23. Mateiko was drafted after putting up 23 goals, 43 points and 20 PIMs in 49 games in 2023-24.