Judge Thokozile Masipa announced the delay in court on the day Pistorius' defence lawyers were due to begin presenting their case after four weeks of prosecution-led testimony and a two-day adjournment.
"One of my assessors is not well, so this court is not properly constituted," Masipa said. "I suggest that we postpone this matter until the seventh of April."
Masipa has two assessors who sit on either side of her in the Pretoria courtroom. South Africa does not have a jury system, and Masipa will deliver a verdict with help from the two assessors, who have limited roles in the day-to-day court proceedings but are there to help Masipa reach a decision.
Pistorius faces 25 years to life in prison if convicted of premeditated murder for killing Steenkamp, and also could be sent to prison for years if convicted of murder without premeditation or negligent killing.
Pistorius says he shot Steenkamp by accident, mistaking her for an intruder in his home and opening fire through a closed toilet door in the early hours of Feb. 14, 2013. Prosecutors say he killed her after a Valentine's Day argument. The world-famous athlete pleaded not guilty to the murder charge and also not guilty to three other firearm-related counts.
After prosecutors wrapped up their case against the Olympian this week, one of the defence lawyers said Pistorius would likely testify.
Legal experts say Pistorius, 27, is expected to testify because he has admitted killing Steenkamp, 29, and must explain to the court why so it can take his version into account. It's common in South Africa for the defendant to be the first person the defence calls, the experts said, unless there are exceptional reasons why another witness should testify ahead of him.
When Pistorius testifies he would also open himself up to cross-examination and likely uncomfortable questions from chief prosecutor Gerrie Nel.