(Reuters) - Stock index futures rose Friday, indicating the S&P 500 may reverse a four-day losing streak ahead of key data on the U.S. labor market.

Labor Department releases the July employment report at 8:30 a.m. (1230 GMT). Employment probably only inched up in July as the economy struggled to regain momentum, strengthening expectations of additional monetary stimulus from the Federal Reserve. Non-farm payrolls likely rose 100,000 last month, according to a Reuters survey, after gaining 80,000 in June.

The S&P 500 index has fallen more than 1.5 percent this week as investor hopes for further stimulus measures from central banks were dampened and a trading error at market maker Knight Capital Group Inc (KCG.N) on Wednesday dealt another blow to confidence in market structure.

The decline comes after the benchmark index saw its best two-day run of the year to close out the prior week as European Central Bank President Mario Draghi heightened expectations for more immediate action to contain the euro zone debt crisis when he pledged to do "whatever it takes" to save the euro.