David Jackson

USA TODAY

Fox News announced Tuesday that Sen. Rand Paul — relegated to the undercard at the Jan. 14 South Carolina debate, which he skipped — will rejoin the main stage Thursday in the GOP debate in Des Moines.

Also on the main stage: Donald Trump, Ted Cruz, Marco Rubio, Ben Carson, Chris Christie, Jeb Bush and John Kasich. (Shortly after the lineup was announced, Trump said he probably won't participate, protesting what he called "wise guy" statements from Fox News about his criticism of moderator Megyn Kelly.)

"To qualify, a candidate needs to be either among the top six in an average of the five most recent national polls, or among the top five in an average of the five most recent Iowa or New Hampshire polls," Fox said in a statement.

As in South Carolina two weeks ago, the preliminary debate will feature Carly Fiorina, Mike Huckabee, Rick Santorum — with the addition of Jim Gilmore, who hasn't made it to the undercard since the first GOP debate in August.

The undercard debate starts at 7 p.m. ET, followed by the the prime-time debate at 9 p.m. ET.

More coverage of the GOP debate:

Bret Baier: We'll treat Trump like other candidates

Fox to Trump: Megyn Kelly will be a debate moderator