Sweeney, a former Reebok and Mars marketer, joined Pentland, the owner of Speedo and Kickers, in January last year with a brief to transform Ellesse into the world's most sensual sportswear brand.
He left the company earlier this year. It is not known whether he had a job to go to and he could not be contacted as Marketing went to press.
Sweeney has been replaced as Ellesse brand president by Andrew Leslie, who reports to Pentland chief executive Andy Rubin. He will take immediate responsibility for developing the marketing strategy for next year's spring and summer collections.
Leslie's previous roles at Pentland include chief executive of Pentland Asia. He has been at the company since 1991 and has been a board director since 2000.
In a statement, the company said: "Sweeney came to help implement the repositioning of the brand and that phase is now complete."