De Gea has not featured for the Red Devils since the end of February, having been excused to attend the birth of his first child.
The 30-year-old Spanish international returned to the United set up for the Europa League round of 16 second leg clash with AC Milan on March 16 but has been on the bench since.
Henderson was once again picked over De Gea in Sunday’s 2-1 Premier League win over Brighton and Hove Albion at Old Trafford.
Henderson has kept four clean sheets in his seven appearances since De Gea’s initial enforced absence and manager Ole Gunnar Solskjaer now faces a dilemma over who to keep between the sticks.
Ferdinand does not envisage De Gea, who has been the club’s number one goalkeeper for the last 10 years, will stay around for too long if a decision does not go in his favour.
“You’ve got two options: you fight for your position or you say, 'that’s me done, I’m off and I’ll go somewhere else,' the former United defender told BT Sport.
“If Dean Henderson finishes the season as No 1, I don’t see De Gea staying there. No chance, I don’t see it. I think he’ll go out now.
“His wages will be a determining factor but at the end of the day, two No 1s doesn’t work.
“De Gea has been a mainstay in the team but Ole is maybe seeing things differently now.
“He’s put Henderson in front of him in the queue. Does De Gea accept that and stay? I don’t think so.
“Henderson has been waiting for this opportunity. Now the pressure is on him. Can he live up to the hype? I’m excited for him and looking forward to see what he can do. Solskjaer has seen something in him but he has to perform now. It’s okay being No 1 at Sheffield United, but it’s a different kettle of fish at Manchester United.
“David will be supporting his team-mate but when he gets home, his pride and ego will be hurting, and if it’s not, he shouldn’t be here. He’s in the prime of his career and he wants to play every week.”
