Joe Jackson said he had a "lot of concerns" over events leading up to the tragedy.
He was commenting as details began to emerge today of results from the post-mortem carried out on his body.
Jackson weighed just 8st 1oz and his stomach only contained partially-dissolved pills when he died, it was reported.
The post-mortem findings, reported in The Sun, state that the singer had four injection marks near his heart, apparently from attempts to pump adrenaline into the organ in a bid to restart it.
Speaking on the Black Entertainment Television Awards (BET) red carpet, Joe Jackson said he could not go into details about what his concerns were.
But Mr Jackson told ABC7: "Michael was dead before he left the house. I'm suspecting foul play somewhere.
"He was waving to everybody and telling them he loves them and all the fans at the gate. A few minutes after Michael was out there, he was dead."
Los Angeles County Coroner's officials said their post-mortem found no indication of trauma or foul play.
But, because of additional tests, an official cause of death could take weeks to determine.
The Jackson family's lawyer said more would be said after the results of a second post-mortem examination.
Mr Jackson said the singer's children were the family's "first priority" and that he and Michael's mother, Katherine, have "authority for our son and his children".
Asked about funeral arrangements, Mr Jackson said: "We haven't got to that yet, we are working on that."
The lawyer representing the singer's doctor, Conrad Murray, said he did not administer the drugs which may have contributed to his death.
Edward Chernoff said: "Dr Murray has never prescribed nor administered Demerol to Michael Jackson. Not ever. Not that day. Not OxyContin (either) for that matter."
It follows reports that the singer received a shot of Demerol - a powerful painkiller - shortly before his death.
Mr Chernoff also discussed how his client found the dying singer.
"He just happened to find him in his bed and he wasn't breathing. Mr Jackson was still warm and had a pulse."
A spokeswoman for Mr Chernoff earlier said that Dr Murray was "is in no way a suspect" after speaking to police officers in Los Angeles at the weekend.
She said the doctor, accompanied by Mr Chernoff, spoke to officers for three hours and "answered every and all questions asked by LAPD in an attempt to help piece together the mysteries surrounding the death of Michael Jackson".
She added: "During the meeting Dr Murray helped identify the circumstances around the death of the pop icon and clarified some inconsistencies.
"Dr Murray has been in Los Angeles since the death of Mr Jackson. He rode in the ambulance to the hospital and stayed at the hospital for hours, comforting and consoling the Jackson family.
"Investigators say the doctor is in no way a suspect and remains a witness to this tragedy.
"Dr Murray will continue to co-operate fully with the authorities and asks that all keep the Jackson family in their prayers."
Los Angeles Police confirmed they do not intend to speak to Dr Murray again but said their investigation was "ongoing".
Jackson topped the album chart last night six years after his last number one as British fans constructed makeshift shrines to remember their idol.
His greatest hits album, Number Ones, took the top spot after a surge in sales saw record shop shelves stripped of his work.
Music retailer HMV admitted many branches had been emptied of Jackson albums since his death following a cardiac arrest at his rented Los Angeles home on Thursday.
Distraught fans who had been eagerly anticipating his planned farewell series of 50 shows at London's O2 Arena travelled from all over the country to gather at various locations in London linked to the star.
Fans pasted posters and lit candles on the windows of HMV in London's Piccadilly Circus.
Meanwhile, family friend and civil rights activist the Rev Al Sharpton said Jackson's family wanted to hold memorials in key cities around the globe.
They were also hoping to hold a memorial service tomorrow at the Apollo Theatre in New York.
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