O'Brien (lower body) isn't in the lineup for Thursday's preseason game against Calgary, per Sound of Hockey.
O'Brien had 28 goals and 93 points in 53 regular-season appearances with OHL Brantford in 2025-26. Seattle's final preseason game will be played in Vancouver on Saturday. O'Brien isn't likely to make the Kraken's Opening Night roster if he's healthy, but the 19-year-old is a highly regarded prospect.