* Madrid mass protests increase tensions in the euro zone * Brazil real flat on central bank intervention fears * Mexican peso 0.2 pct lower; Chilean peso down 0.1 pct RIO DE JANEIRO, Sept 26 (Reuters) - Latin American currencies fell slightly on Wednesday as growing opposition to austerity measures in Spain added to jitters over the euro zone debt crisis, tempering investors' optimism on recent stimulus measures in the United States. The Mexican peso lost 0.2 percent while the Chilean peso dropped 0.1 percent as investors turned more averse to emerging markets risk in general. The Brazilian real was near flat, however, in a seventh consecutive session of very low volatility. Worries about the future of the euro zone grew as mass protests against austerity measures erupted in Madrid, making it more difficult for Prime Minister Mariano Rajoy to request international financial aid -- a condition for Spain to receive support from the European Central Bank. Investors fear that a delay in the ECB bond-buying program would further complicate the euro-zone debt crisis, potentially dragging more economies into recession. "Markets are really bad out there. The losses are triggered by Spain, which is delaying its request for financial assistance," said Rodrigo Sarria, a trader at Celfin Capital in Santiago. He added that the Chilean peso could weaken to around 474.00 per dollar in the short term. Chile's currency last traded at 470.60 per dollar. Despite a possible short-term weakening, the peso remains set to gain in the medium term as U.S. stimulus measures increase dollar inflows to emerging markets, said Sarria. In Brazil, the real was little changed for yet another session as investors refrained from making bigger bets in a market that remains under constant threat of central bank intervention. Brazilian policymakers have bound the real to a very narrow trading range of 2.0 to 2.1 per dollar as they vow to use all means necessary to offset capital inflows resulting from the U.S. Federal Reserve's stimulus measures. "Investors got scared with all this intervention talk," said Gustavo Godoy, manager of the treasury desk of Daycoval bank in Sao Paulo. "You have the whole world to invest your money, why bring it to a market that is subject to intervention?" Concerns with the global economy drove Brazil's interest-rate future lower for the fifth consecutive session, showing a growing number of investors are betting the central bank will cut the country's base Selic rate again in October. At least half of the bets are for a 0.25 percentage point cut in the Selic in October, the interest-rate curve shows . Earlier this month, the curve showed most investors betting that Brazil's monetary easing cycle was over. Latin American FX prices at 1600 GMT: Currencies daily % YTD % change change Latest Brazil real 2.0325 -0.09 -8.07 Mexico peso 12.8845 -0.19 8.42 Argentina peso* 6.2700 0.80 -24.56 Chile peso 470.5000 -0.11 10.37 Colombia peso 1,798.1500 -0.06 7.80 Peru sol 2.5960 0.00 3.89 * Argentine peso's rate between brokerages