Niemi has been reminiscing about his time at Craven Cottage and Sunday's opponents Southampton in an exclusive interview with the club's official website ahead of this weekend's game.
The ex-Finnish international, who now coaches his country's goalkeepers, is particularly impressed by the form of his successor between the sticks in west London as he continues to defy his advancing years, with just two days to go until turns 40.
He said: "Mark's been at the top of his game for 15 years now - he's a goalkeeper I admire so much and he proves it's not about your age. It's about how they play and obviously they've been injury free which helps a lot.
"When I watch Schwarzer play I think he looks like he's getting better and better. You'd think that a goalkeeper would hit their peak in their 30's but he's unbelievable.
"I have to say he's so fit - I'm jealous because he looks marvellous when he's standing in that goal! Once he finishes his career, whenever that will be, people will look back and say he was one of the best."
Niemi, who is only a few months older than Schwarzer, has admitted he will have divided loyalty when the two teams clash at St Mary's on Sunday, as he has fond memories of his time with both clubs.
He added: "It's going to be a funny feeling on Sunday knowing who to support. It's really difficult for me and I just hope it's a cracking game that ends in a 3-3 draw. I want to see lots of goals, excitement and a draw to make me happy! That's my wish!"