Powell was dealt a major blow after being omitted from Warren Gatland's squad for a second 10-day training camp in Poland.
He instead linked-up with new club Sale Sharks, while Gatland jetted Gareth Delve to the boot camp in Spala, in his place.
Melbourne Rebels vice-captain Delve, 2005 Lion Ryan Jones and Toby Faletau are now the front-runners to fill the No8 berth in New Zealand.
But Powell, who has never featured in the showpiece tournament, is determined to regain his place.
Wales returned from Poland yesterday and face England at Twickenham on August 6, in the first of back-to-back matches.
And the Lions backrower is aiming to impress against Martin Johnson's men in a bid to revive his World Cup hopes.
"I've definitely not written off my chances. I like to think I'm still in contention," said 29-year-old Powell.
"The World Cup is a dream for every rugby player. If it happens, great.
"We've got England in two weeks and I'm keen to impress. I'm training hard and, if the chance comes up, I will grab it with two hands.
"But my main goal for the time being has to be on training well with Sale and ensuring that if the Welsh thing comes up I will be ready for it."
Powell has not played for Wales since winning his 17th cap in the opening 2011 Six Nations defeat to England.
He found himself in hot-water with Gatland after being attacked in a London bar while still at Wasps in April.
Powell then missed Wales' clash with the Barbarians in May before being recalled to Gatland's 45-man preliminary squad ahead of the World Cup.
But Gatland insists the door is still open for Powell to claim a place in the September tournament and he will have that opportunity against England and Argentina next month.
Gatland will then select a final 30-man party on August 22, before the squad departs for New Zealand.