Here's how the markets will react to the health-care vote, according to Art Cashin

Wall Street could wake up to a massive sell-off or rally Friday depending on how the House votes on a key Republican-led health-care bill, Art Cashin told CNBC on Thursday.

The House is scheduled to vote Thursday on The American Health Care Act, a bill that would dismantle the Affordable Care Act, better known as Obamacare, and could dramatically impact health insurance for tens of millions of Americans.

Cashin said most presume that the vote will happen after the U.S. market closes, which will allow investors to "rethink and mute."

"If they call for a vote early, that means they think they've got the votes and that's why you'll see a little bit of a rally going into it," the UBS director of floor operations said on "Squawk on the Street."

"If they decide to postpone and not vote either tonight or whatever, [there'll] be a mild sell-off because people say the votes still remain questionable. If they vote and have it voted down, there will be a more substantial sell-off," he said.

Cashin added if the House passes the vote, there will be a rally.

U.S. stocks traded in a narrow range on Thursday as Wall Street awaited the vote. The House vote is seen as a crucial part of President Donald Trump's agenda. Trump has said that the repeal and replacement of Obamacare must happen before other plans, like a tax overhaul.

U.S. equities closed mixed Wednesday ahead of the vote. Cashin said that investors' attention was diverted by the deadly London attack near Parliament.

On Tuesday, stocks had the biggest one-day drop since before Trump won the election, on concerns about opposition to the bill.

— CNBC's Fred Imbert and Reuters contributed to this report.