The Dutch shot-stopper has been in the game since the late 1980s after beginning his illustrious career with Ajax.
The 39-year-old has since played for the likes of Juventus and Fulham before pitching up tent at Old Trafford in 2005.
Van der Sar has won everything in the game from Champions League to Premier League titles, although a FA Cup winners' medal remains absent from his trophy cabinet.
Steele feels the veteran has already made up his mind to hang up his gloves next summer, but he remains keen to bow out winner having help win the FA Cup.
"I think Ed has made his mind up and said this is his last year," he told the Manchester Evening News.
"He hasn't won (the FA Cup) and that is a big target for him. He has won most things in the game, there is not much left he hasn't.
"When we rotate our goalkeepers, I think you will see Mr Van der Sar knocking on the door and asking the boss to play in the FA Cup."
However, Steele does not feel Van der Sar's possible retirement is not set in stone and believes it could be of benefit to United for the shot-stopper to stay on.
The Red Devils have the likes of Tomasz Kuszczak and Ben Amos waiting in the wings, although Steele feels Sir Alex Ferguson's troops are still in transition.
"I think we need him because this team is in transition at the moment," he said.
"If he gets to Christmas and he thinks it is right to go on and the manager thinks it is right we will make a decision.
"It is down to how he feels and performs. If he doesn't perform the manager will make the decision. Edwin will as well."
Another player who has set a timescale on his career is striker Dimitar Berbatov, who does think he will be playing into his mid-30s like veteran team-mates Ryan Giggs, Paul Scholes and Gary Neville for fear of making a fool of himself.
"Me? At 35? No way!" the 29-year-old told Inside United.
"Seriously, though, everyone is different and you have to know your body is giving you the signals to stop.
"Having been here for two seasons, I know why Giggs, Scholes, Neville have been here for so long and why they are still playing. Here they have the facilities and the coaching staff who know how to prepare you.
"Obviously you need to focus on the football and when you go home, you have to be professional and know how to live your life. I see all these things in these three guys, especially.
"They are still playing at the highest level, so I think to myself, 'Can I do that?' If not, then at least try to see how long I can play for.
"But when your body tells you, that's when you have to stop and not make a fool of yourself."