The Sunderland frontman is facing at least six weeks on the sidelines after damaging a thigh muscle ahead of Monday night’s Tees-Wear derby.
The twice-capped 26-year-old, who has scored five goals in seven Sky Bet Championship appearances for the promoted Black Cats this season, was forced to withdraw from the team for the 1-0 defeat at Middlesbrough after sustaining an injury in the warm-up.
A scan has revealed significant damage and the former Ross County hitman now faces a period of rehabilitation which could keep him out for between six and eight weeks.
Head coach Tony Mowbray told the club’s official website: “Ross will be out for six to eight weeks – it could be a little longer, but that will depend on his rehabilitation and the way his body reacts.
“He’s a really positive guy and we hope that he will be a quick healer, so we will take it game by game and hopefully he returns quickly.”
Stewart made his international debut earlier this year, appearing as a substitute in a Nations League game against Armenia on June 8 before doing likewise in the 3-0 defeat to Ireland in Dublin three days later.