The U.S. Supreme Court on Tuesday halted the execution of a Missouri man until an appeals court can decide whether the lethal injection could drug cause seizures due to his medical condition.

Ernest Johnson, 55, was convicted of bludgeoning three people to death in 1994 and was scheduled to be put to death at 6 p.m. Tuesday at the Missouri state prison in Bonne Terre, reported The Associated Press.

He suffers from a benign slow growth brain tumor that was partially removed in 2008, leaving him with a hole in his skull and missing up to 20 percent of his brain. His attorneys argue that the lethal injection drug Pentobarbital could cause painful seizures and excruciating pain, which they say would be in violation of the Eighth Amendment's ban on cruel and unusual punishment.

His attorneys also say that Johnson is mentally disabled with an IQ score as low as 63, and he should therefore be spared from execution, according to AFP.

The Supreme Court granted a stay request pending an appeal before the 8th U.S. Circuit Court of Appeals, saying, "The application for stay of execution... is granted pending the disposition of petitioner's appeal."

"In the currently pending appeal, the Court of Appeals will be required to decide whether petitioner's complaint was properly dismissed for failure to state a claim or whether the case should have been permitted to progress to the summary judgment stage."

One of Johnson's attorneys, Jeremy Weis, said after the ruling: "We are very pleased by the Supreme Court's Order granting the stay for Ernest, and we look forward to continuing to litigate Missouri's execution protocol in the courts," according to NBC News.

A court in Missouri ruled last week that Johnson's execution could be so painful that it would violate the Constitution, but Johnson did not propose any alternative that would allow his execution to proceed quickly, so the appeal was rejected, according to AFP.