A key centrist Democrat on Tuesday signaled the "opt out" addition to the Senate's public option proposal might not be enough to win her vote once healthcare reform reaches the chamber's floor.

Sen. Blanche Lincoln (D-Ark.) has long maintained that she would not support any government-based healthcare plan, citing concerns with its projected costs. But her line on Tuesday -- delivered a day after Senate Majority Leader Harry Reid (D-Nev.) debuted his "opt out" public option plan -- nonetheless calls into question whether Democrats have enough votes to pass their bill once it reaches the Senate floor.

"Creating another government-funded option is not where we're going. We don't need to go there," Lincoln said Tuesday during a video conference, as reported by ABC.

"If you have to opt in, then it takes a while to create that pool, that mass of people, so if states are opting in it takes a while for states to create that critical mass of people that brings down the cost," she said. "But opting out is a problem, too, because again you have to wait until legislatures meet and other things like that."

If Lincoln ultimately does not support the newly retooled public option -- or, if she chooses not to support Democrats during a cloture vote -- it could spell serious trouble for the majority party.

Already, Reid and his colleagues are scrambling to brace for Sen. Joe Lieberman's (I-Conn.) potential filibuster, which he announced today. If Lincoln threatens to dissent in a similar fashion -- choosing to vote against cloture when the time comes -- it is unclear how Democrats will make up the lost votes.