Oscar Pistorius has arrived at court in Pretoria where a judge will rule whether the athlete must undergo psychiatric tests.
The prosecution made the application for a referral after defence evidence from a forensic psychiatrist, who said the defendant had generalised anxiety disorder.
But the defence argue there is no need for psychiatric observation, and said the application had “no merit”.
If approved the move could delay the trial by at least a month.
The prosecution has already claimed the decision to call Dr Merryl Vorster so late in the trial – after Pistorius himself had given evidence – may be a “fallback option” for the defence in the event of a guilty verdict.
Sending the 27-year-old for mental health tests at this stage could also eliminate the possibility of an appeal by the defence on the grounds that Pistorius’ mental health had not been fully and adequately assessed.
If Pistorius were found to be suffering from a mental illness, he could be held not criminally responsible for his girlfriend Reeva Steenkamp’s death and found not guilty by reason of “mental illness or intellectual disability”.
In her evidence, Dr Vorster said Pistorius had GAD and was a “distrusting and guarded” person who is “hyper-vigilant” about security.
But she also said he was able to able “to function at a high-level”, and did socialise.
Pistorius is accused of killing Ms Steenkamp in a premeditated attack at his home in Pretoria, South Africa, on Valentine’s Day last year.
He denies the charge and claims he shot his partner after mistaking her for an intruder.