The former world heavyweight boxing champion's friends became concerned after he began acting paranoid and "strange", before calling mental health experts.
"He was acting really strange," a source told The Sun. "He had become convinced that anyone he talked to was trying to take his money. It's really sad because everyone loves Frank and we are all hoping he gets better soon."
The boxer was sectioned under the Mental Health Act 1983 in 2003, before later being diagnosed as bipolar.
Police and doctors arrived at Bruno's home in Bedfordshire on Wednesday (April 11), but he was not in at the time. However, the following day he willingly admitted himself to a health facility.
Bruno's agent Dave Davies said: "Frank hasn't been sectioned. He started showing tendencies of bipolar. From what I understand he went of his own accord into a clinic.
"He needs a couple of weeks' good rest. He is absolutely shattered. With his condition, Frank needs to take more care of himself.
"When he comes out of his house every morning, he is on show. He doesn't criticise that or moan because it is the public that have put him where he is. But as an outsider watching Frank non-stop, I feel he needs a good rest.
"Sometimes we all need a few days off to recharge our batteries. That's what Frank is doing."
Frank Bruno was rumoured to be taking part in 2010's edition of Strictly Come Dancing, but this failed to materialise.
He became world heavyweight champion in 1995, before becoming a fan favourite for his appearances in pantomimes around the UK.