The 29-year-old made it into Wales’s training camp in Spala, Poland, but was dropped when the 45-man squad was trimmed down to 35.
The Welsh back row remains a competitive area, with players such as Ryan Jones, Toby Faletau, Dan Lydiate, Josh Turnbull, Rob McCusker and Justin Tipuric all vying for places in Gatland’s final selection.
“My focus now is playing for Sale and the Welsh thing is at the back of my mind,” Powell said. “But all I can do is keep training hard and if it comes along I'll grasp it with two hands."
Wales face England in Twickenham and again at home in Cardiff as part of their World Cup warm-ups, before completing their preparations with a game against Argentina.
Gatland’s final 30-man squad selection is due on August 22.