The Scot, who has guided the club to 12 English league titles, two European Cups and five FA Cups, celebrated 25 years in the United hot seat last month.
"I think I've got three years at the club," he told Manchester United television. "As long as my health stays up, and as long as I'm still enjoying it and still getting the satisfaction of the team doing its best."
Asked if he was still motivated by the challenge of new achievements, he replied: "Yes. There are new players that have come in, like [Phil] Jones, [Chris] Smalling, Ashley Young, [Danny] Welbeck... and they haven't won any league medals yet.
"We have to continue the dominance of winning leagues and, without question, winning a European Cup is important at this club.
"We should have been in at least another three finals. But you can't be greedy, I suppose, and having won two in my time is an achievement. They were special, it was terrific to win them. I think I'd be very keen to do that [again]."
It is not just City who pose a threat to United's hopes of retaining their league title with Ferguson telling local media that Tottenham Hotspur have emerged as genuine contenders.
"Tottenham at the moment are the best team in the country. Their form at the moment is the best anywhere and they are definitely title contenders," Ferguson, who led United to a record 19th league title last season, was quoted as saying.
"We've had the stats which say we are five or six points ahead of previous years' form at this time of the year. But you have to say that City's form is equal to that. To have 45 points is an enormous total at this point of the year.
"It will be nip and tuck between the two clubs, but Tottenham are the best team in the country at the moment."
