(CNN) President Donald Trump's top economic adviser said Thursday night he's confident Republican Sen. Marco Rubio will ultimately be a "yes" on the GOP tax bill despite the senator's threat to vote against the legislation unless there is a more generous child tax credit -- a threat that could leave Senate Republicans with no room for error with their slim 52-48 majority.

"I've been pretty consistent in my communications on this issue and that is I want us to see the refundable portion of the child tax credit increased from its current number," Rubio told reporters earlier in the day on Capitol Hill. "If it stays at $1,100, I'm a 'no.' Let's hope it doesn't."

During an interview on CNN's " Erin Burnett OutFront ," White House Council of Economic Advisers Chairman Kevin Hassett said Rubio's concern is "something that the people in the Senate will have to work out with Sen. Rubio."

He went on to predict that there would be an agreement and cautioned, "I don't think anyone thinks Rubio is going to hold up this bill."

However, Hassett tried to walk a fine line, defending the current child tax credit proposal without criticizing Rubio.

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