Stock futures mixed on "fiscal cliff" worries

Stock futures were mixed on Thursday as a new round of stimulus for the economy was not enough to offset worries over the impact of the impending "fiscal cliff".

* Sprint Nextel Corp is looking to buy Clearwire Corp stock it does not already own for $2.90 per share, it said in a regulatory filing. Shares of Clearwire were up 5.5 percent at $2.90 in premarket trading.

* Knight Capital Group Inc expects to make a decision on its future ownership by early next week, the Wall Street Journal reported, citing people familiar with the matter.

* Australia's GrainCorp Ltd rejected a sweetened $2.9 billion bid from Archer Daniels Midland Co . Analysts said ADM was likely to lift its bid for the company.

(Reporting by Leah Schnurr)