The 38-year-old Welshman celebrated the landmark by scoring an injury-time winner in his side’s clash with Norwich on Sunday.
"For a player to play for one club for 900 games is exceptional and it won't be done again.” Ferguson told BBC Sport.
"We were lucky today. Norwich were the better team.
"In the first half they put 12 crosses in and we had to defend well and the keeper was excellent. They were always in the game and we only played to our level for five or six minutes after they scored."
Giggs, who is in the hunt for his 13th Premier League medal with Manchester United this season, is expecting this year’s title race to be the tightest in history.
"We know how important a time it is, City put pressure on us yesterday and we knew we had to win," he said.
"To play 900 games for this club, who I've grown up supporting, is special - it's a great day for me. I am sure there will be more twists and turns in the title race and I expect more drama and late goals."
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