The media company is expected to invite agencies to pitch for the business following differences with its incumbent.
Sky appointed i-level to work across its online media business in May 2005, with a brief to help grow subscriber numbers. However, the relationship is said to have deteriorated in recent months.
In March, Sky called a pitch for its search business, which resulted in the appointment in August of Diffiniti to handle search engine optimisation activity and Unique to work on pay per click.
Sky's online spend has increased as a result of its battle for subscribers with Virgin Media and as part of large scale campaigns such as "See Speak Surf" and "Believe in Better".
Its online activity is a key part of its constant work to increase subscriber levels. In the year to 30 June, Sky added a net 406,000 customers, taking it to a total of 8.6 million.