U.S. stock index futures slipped further on Wednesday as investors turned cautious after data showed private-sector jobs losses were higher than expected in July, sparking concern about the strength of the economic recovery.

* The ADP employment data came two days before the release of the government's all-important non-farm payrolls report for July.

* S&P 500 futures shed 2.5 points and were near fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures dropped 37 points, and Nasdaq 100 futures slipped 3.0 points.

(Reporting by Ellis Mnyandu; Editing by Padraic Cassidy)