The Dutch veteran, 37, kept another clean sheet at Wigan Athletic on Sunday to help United retain the Premier League title.
As part of The Red Devils' rock-solid defence, the former Fulham shot-stopper will be hoping to fend off the challenge of Foster and Tomasz Kuszczak once the 2008/2009 campaign comes around.
"His experience is so important to us," Ferguson told Voetbalzone.
"You can see that he's played more than 120 international matches for the Dutch national team.
"Edwin radiates calm and is confident of his own abilities.
"And that spreads to our defence.
"If he continues to perform as he does, he can play for another year or two as his age doesn't bother me."