WASHINGTON (Reuters) - U.S. Senate Republican leader Mitch McConnell, speaking as lawmakers prepared to vote on a bill to address Puerto Rico's financial crisis, warned on Wednesday that failure to pass the legislation by Friday could lead to a taxpayer funded bailout.

"This is the best and possibly the only action we can take to help Puerto Rico," McConnell said on the Senate floor amid uncertainty over whether the legislation would receive the support needed in a critical procedural vote due at 10:30 a.m. EDT.

"Doing nothing now ... (is) the surest route to both a taxpayer funded bailout of Puerto Rico and a humanitarian crisis for its people," he said.

(Reporting by David Morgan; Editing by Chizu Nomiyama)