Luke Donald will team up with fellow Ryder Cup player David Howell for England's World Cup title defence in November at Vilamoura, Portugal.
Donald was Casey's selection last year
Donald triumphed in last year's event with Paul Casey.
Each nation's leading player can select their partner, but their choice must also be ranked in the top 100.
Donald, at number 14, was England's leading player in the world rankings on 19 September with Howell 19th while Casey was back in 62nd.
"My first step was to discuss the situation with Paul and he fully understood that I wanted to make my decision based on current form," said Donald.
"I have spoken to David and he is looking forward to representing England in Portugal. We both feel that we have a great chance of defending the trophy."
Casey and Donald earned England a one-shot victory over hosts Spain in 2004 after firing an eight-under-par 64 in the last-day foursomes.
The 18 nations who have qualified for this year's event are the US, Fiji, South Africa, Spain, Australia, Argentina, Ireland, England, New Zealand, Denmark, Scotland, Canada, Sweden, South Korea, Japan, Germany, France and Paraguay.