The football star-turned-actor, 77, has been treated at the Santa Monica hospital in California, but was recently discharged to receive hospice care at home.
The former Detroit Lions player has been battling cancer and dementia, and recently suffered kidney failure.
Karras' close friend Tom McInerney tells the Detroit Free Press the star's wife, Susan, told him about his pal's health crisis last week (ends07Oct12) and fears he hasn't got much longer left to live.
He says, ""(His kidneys) gave out on him and (his) legs swelled up and his ankles swelled up and arms, so she (Susan) said it doesn't look good. They figured probably a couple weeks (to live).
""He said, 'I want to go home,' so knowing Alex she made arrangements for him... She called me this morning, (and) said, 'It doesn't look too good, Tommy. They're talking probably a couple days.'
""She said if you came out here it wouldn't be worth his while because right now he's talking about he wants to see his (deceased) mother and dad, and he's on morphine, he's on oxygen. She said it's maybe a couple, three days at the most.""
A statement from Detroit Lions president Tom Lewand reads, ""The entire Detroit Lions family is deeply saddened to learn of the news regarding the condition of one of our all-time greats, Alex Karras... We join his legions of fans from both sports and entertainment in prayer and support for Alex, his wife Susan, and his entire family during this most difficult time.""
Earlier this year (12), Karras filed a lawsuit against America's National Football League (NFL) bosses, alleging they failed to protect him from the concussions he suffered as a Detroit Lions player.
He joined hundreds of other former NFL stars in a class lawsuit seeking medical monitoring, cognitive health benefits and financial compensation.