The loss to Kell brook could be his last fight, as he fears taking more punishment and wants to spend more time with his family.
One of the most bitter rivalries in British boxing was settled in the sixth round.
Speaking after the fight at Manchester Arena, 35-year-old Khan said he had been in the game for a long time.
He said that he had done more than he expected.
Maybe I peaked too early. I won the world title at 22. I have been in the game for a long time.
I am an old man. I want to spend time with my family.
After two punishing right uppercuts followed by a left hook in the sixth, the referee waved off the contest, as Kell Brook had Khan on wobbly legs from the first round.
Khan said retirement was definitely an option.
Khan said he would sit down with his family but that it could be his last fight.
I want to retire from boxing, I have always said that.
I know I showed a big heart and took some big shots, but sometimes too much punishment can be harmful in the future.
After all of the heated build-up to a fight between former world champions that had been 17 years in the making, Khan praised his opponent.
Kell put on a great performance and the better man won. He removed his skin. I didn't expect that from him.
I had the best training camp for the fight. I don't want anyone to blame his coaching team because they did everything they needed to.
I put my hands up and took full responsibility. We did not leave any stone.
Kells said he would fight again if it was the right fight.
After years of chasing the fight, the 35-year-old admitted Khan had become someone he despised, but the pair shared an embrace inside the ring after the fight.
The pleasantries continued in the news conference.
He has won world titles and been involved in some big fights.
He will have to sit and see if we want to continue.
We share the ring and I think we are all right now.
Immediately after the fight, he said that he could live in peace with Khan on his record.
I love this game and my mojo is back. We will listen to loved ones, but I am back.
I can walk away, but I could fight Chris. I don't like him. I will fight if the fight is right.