By Sweta Singh
(Reuters) - U.S. stock index futures were lower on Friday amid worries about Greece's ability to strike a deal with its euro zone partners by Sunday and ahead of U.S. gross domestic product (GDP) data.
* A euro zone official said Greece will not be able to get the money still available under its current bailout plan if it does not agree to the outline of a such a deal by the end of the week.
* The Commerce Department is expected to report U.S. economy likely shrank in the first quarter instead of growing, as was estimated last month. The data is due at 8:30 a.m. ET (1230 GMT).
* While several economists have cast doubts on the accuracy of GDP estimates for the quarter, investors will peruse the data for clues to narrow down the timing of an increase in interest rates.
* With growth estimates so far for the second quarter around 2 percent, the economy appears poised for its worst first half performance since 2011.
* The GDP report is also expected to show a second quarterly drop in corporate profits because of the strong dollar and oil prices.
* Altera
* Splunk
* Heron Therapeutics
Futures snapshot at 7:34 a.m. ET (1134 GMT):
* S&P 500 e-minis
* Nasdaq 100 e-minis
* Dow e-minis <1YMc1> were down 13 points, or 0.07 percent, with 21,835 contracts changing hands.
(Additional reporting by Sayantani Ghosh in Bengaluru; Editing by Savio D'Souza)