The top seed, who is playing the ATP 250 clay event at altitude for the first time since he won it in 2004, will Thursday play his opening match after a bye against either German Daniel Brands or longtime friend Marco Chiudinelli.
Federer began testing a larger 98-square-inch racquet last week in Hamburg, reaching the semi-finals before losing to number 114 Argentine qualifier Federico Delbonis.
He said he needs more time and matches to make a final decision on the prototype model.
"So far, I'm happy with this change,"said the 17-time grand slam champion.
"But I need many hours on the court to see if this is a good decision," he said.
"I haven't yet taken the decision on whether to use it in the US (he begins his pre-US Open campaign in a fortnight at the Montreal Masters). "
Federer said he still needed to think it over.
"There are players who have experienced" problems when they changed racquets, Fernando Verdasco and to some extent Novak Djokovic."