Khan was floored three times as American Garcia exploited the Englishman's naive tactics to keep his WBC light-welterweight title and snatch his opponent's WBA belt.
It was Khan's second straight defeat following his loss to Lamont Peterson and the third in his career, having also tasted defeat at the hands of Breidis Prescott.
Froch, the current IBF super-middleweight champion, revealed today [Sunday] he would hang up his gloves if he was in the Bolton fighter's shoes.
"I would retire if that happened to me," he told Radio 5 Live's Sportsweek programme.
"Why? Because I am not in this sport to get beaten, knocked out, or outclassed.
"I've lost twice, I lost a very, very close points decision to one of the best pound-for-pound fighters in the world in Andre Ward and I've come back and beaten an unbeaten fighter, Lucian Bute, the very next time so I'm world champion.
"If I had lost to Lucian Bute I would probably have retired, because I am in this game to be at the very top and stay at the top. I'm not in this game to make up the numbers.
"It's a personal decision whether or not you retire, but to get stopped in the fourth round and to be previously knocked out, it's just very, very damaging."