The money was given in February and brings his total contributions to Gingrich's presidential efforts to more than $16 million.

Some have speculated that it's the last cash the super-PAC will see from its largest donor.

Gingrich trails badly in the polls, and has only won two primaries — in South Carolina and his home state of Georgia. The former House Speaker staked his campaign on a “Southern strategy,” but finished second to Rick Santorum in Mississippi and Alabama last week.

The former House Speaker has vowed to stay in the race until the Tampa, Fla., convention in August, and denies that he’s only being kept afloat by the large donations from Adelson.

“I have 176,000 supporters at — they want me to stay in the race. I really represent their interests as individuals," he told CBS last week, claiming that "95 percent have given less than $250" — meaning they haven't hit their legal limit and can donate more.

On Tuesday, the Gingrich campaign said it raised $2.5 million in February, the least of the four remaining GOP candidates, and the campaign spent $2.8 million, leaving it $1.5 million in debt.