The office of United States Senator John McCain said he "looks forward" to his return to the chamber on Tuesday.

"Senator McCain looks forward to returning to the United States Senate tomorrow to continue working on important legislation, including health care reform, the National Defense Authorization Act and new sanctions on Russia, Iran and North Korea," a statement from his office read.

The Senate is to vote Tuesday on whether to open a debate on whether to repeal and replace former president Barack Obama's health care law. Senate majority leader Mitch McConnell has promised an open amendment process and a "robust" debate.

McCain, 80, was diagnosed with a malignant brain tumor and underwent blood clot surgery last week. His return to the Senate had been uncertain.

With Republicans holding a 52-seat majority in the 100-seat Senate, McCain's vote could be critical to the start of the process to repeal the law, commonly referred to as "Obamacare." All Senate Democrats are expected to be opposed.

Several Republicans have either publicly opposed or criticized previous health care reform efforts from their party. McConnell has stepped back twice from anticipated votes to reform the bill.

"I think we're going to proceed to debate," Senator John Cornyn from Texas said. However, he acknowledged about McCain: "It would help if he's here."

Trump: 'Chance to keep their promise'

McCain's return is good news for US president Donald Trump, who called the American health care law "death" in a public address on Monday. He also mounted considerable pressure on his Republican colleagues in the Senate to repeal and replace the law, which has been a common Republican platform in recent years.

"For Senate Republicans, this is their chance to keep their promise. Over and over again, they said, 'Repeal and replace, repeal and replace.' But they can now keep their promise," Trump said, surrounded by some he called "victims" of the health care law. 

Trump then jokingly threatened his Secretary of Health and Human Services Tom Price while speaking to Boy Scouts in the nearby state of West Virginia later on Monday.

The American president said Price would lose his job if he did not get the votes to start the health care debate.

"By the way, you gonna get the votes?" Trump said, turning to Price. He added: "He better get 'em. Otherwise, I'll say: Tom, you're fired."

"You're fired" was the catch phrase Trump used on his reality television show "The Apprentice." Trump gave Price a friendly-looking tap on the shoulder after the remark.

dv/kl (AP, Reuters)