"There was that possibility because of the fact that his contract was up," said Ferguson on Sky Sports News, when asked if he thought the England international would move on.
Ferguson also praised the impact of Carrick, who has steadily grown in stature since joining United from Tottenham in the summer of 2006.
The United boss added: "He has had a wonderful season, he's been a terrific buy and I'm really very pleased with him.
"He's a good age, he's a nice age, so we're all happy about all these things."
In addition to extending the contracts of three current players, Ferguson also admitted he is likely to add to his squad in the summer.
"This continues our policy of lengthening the contracts at the right times and it gives us continuity of the first-team squad together, which we try to work hard at, and that's not easy in today's world, but we do our best," continued Ferguson.
"We have a strong squad, whether we stock up in the summer, then it's a possibility of course, a good possibility, but there's no question that having that strong squad has definitely aided us this season."