Former U.S. House speaker Newt Gingrich is due to officially suspend his bid for the Republican presidential nomination, after winning just two state primaries and amassing more than $4 million in campaign debt.

Gingrich thanked his supporters in a video message ahead of Wednesday's announcement, but did not mention presumptive Republican nominee Mitt Romney.

He did, however, warn about Romney's opponent in the November general election, saying giving a second term to President Barack Obama, a Democrat, would be “a genuine disaster.”

A spokesman for Gingrich said last week the former congressman will endorse Romney.

Gingrich emerged as a strong contender after winning the South Carolina primary in January, but his campaign faltered after he lost the following primary in Florida. His only other primary election win came in March in his home state of Georgia.

Gingrich's withdrawal leaves Texas Congressman Ron Paul as the only other candidate in the Republican race, but he is far behind Romney in the delegate count.

Gingrich plans to focus on helping Republicans seize control of the Senate while maintaining their majority in the House of Representatives. He masterminded the Republican takeover of the House in 1994.