Ferguson was paying tribute to Giggs after the Welshman marked the milestone with a stoppage-time goal that gave his side a 2-1 victory over Norwich City in the Premier League.
"For a player to play for one club for 900 games is exceptional, and it won't be done again," Ferguson told the BBC. "He deserved that goal for his service to the club. He's had an amazing career and he's an amazing man."
Giggs arrived at the far post two minutes into stoppage-time at Carrow Road to tap in Ashley Young's cross and keep United in touch with league leaders Manchester City.
The 38-year-old made his debut for United in 1991 and has played more times for the club than anyone else.
Earlier this month Giggs, who has won 12 Premier League titles, four FA Cups, three League Cups and two Champions League winners' medals, signed a one-year extension to his contract.
"To play 900 games for this club, who I've grown up supporting, is special - it's a great day for me," Giggs said. "I am sure there will be more twists and turns in the title race and I expect more drama and late goals."
Giggs's strike and an early header by 37-year-old Paul Scholes ensured City's lead at the top was kept to two points after their 3-0 win over Blackburn Rovers on Saturday.
"We know how important a time it is," Giggs said. "City put pressure on us yesterday and we knew we had to win.
"Right through the squad, for all the time I've been here, we've always had that ability to not give in and score late goals."
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