Oscar Pistorius, 26, was a “broken man” after rising legal costs forced him to sell his belongings, Mike Azzie said.
Meanwhile, lawyers for the Paralympic champion have filed an appeal to ease his bail restrictions.
Oscar Pistorius, who is on trial for shooting model Reeva Steenkamp at his home last month, denies the charges of premeditated murder, saying he mistook her for an intruder.
The athlete was released on bail on February 22 and is due to appear in court again in June.
Mike Azzie, who has known the athlete since childhood and has been in regular contact with him, said he was worried about his mental and emotional state.
He said the Paralympian had been forced to sell his racehorses to cover the spiralling legal fees.
“He has no confidence in his tone of voice and he is almost like someone that is walking around in circles and doesn’t know where he is going,” Mike Azzie said in the forthcoming BBC3 documentary, Oscar Pistorius: What Really Happened?
“I would say that, just speaking to him, he is a broken man. I would go as far as to say that he could be on the verge of suicide. It really worries me.”
Mike Azzie added that Oscar Pistorius frequently talked about Reeva Steenkamp and her family.
“He just always seems to mention Reeva and asks us to pray for her and her family,” he said in the interview, due to be broadcast on Monday.
“But most of all, you’ve got to understand that we are there for him and we will always be his friend.”
Police said they were still going through a large number of texts recovered from Reeva Reevenkamp’s mobile phone.
Service providers have been asked to make available all records of phone calls and messages exchanged between the model and Oscar Pistorius on the night of the shooting, police said.
Meanwhile, defence lawyers have sought to ease bail restrictions imposed on Oscar Pistorius, according to papers released by his family on Monday.
The court had ordered Oscar Pistorius to hand over his passport, avoid his home in Pretoria and report to a police station between 07:00 and 13:00 every Monday and Friday.
But his lawyers said the conditions were “unwarranted and not substantiated by the facts”.
Evidence presented at the trial showed Oscar Pistorius was not a flight risk, and should be allowed to travel outside South Africa with official permission, they argued.
Reeva Steenkamp, 29, died after the athlete fired multiple shots into the toilet of his apartment in a gated housing complex in Pretoria on February 14.
Oscar Pistorius bail conditions:
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