De Gea has reportedly agreed a six-year contract extension at Manchester United.
The Spanish international is set to become the world’s highest paid goalkeeper.
De Gea will earn around £375,000-a-week at Old Trafford to end speculation over his future.
And Toloui reckons that means Henderson will be allowed to leave on loan again for the upcoming season.
Henderson started all 46 Championship games on loan at Sheffield United last season as they got promoted back to the Premier League.
“The knock on [to De Gea’s contract], Dean Henderson gets his Premier League loan to Sheffield United probably off the back of this as well,” Toloui said.
“So not only have they got David de Gea locked down for the next few years, they’ve potentially got their replacement or long-term goalkeeper strategy, and [Sergio] Romero as well.
“They’re stacked in the goalkeeping department.”
However, Blades boss Chris Wilder has revealed doubt he has over a return for Henderson.
He admits he is looking at alternative options as the deal is taking longer than expected.
“[It] isn’t progressing at the pace we’d like,” Wilder told The Star.
“He wants to come, the football people at Manchester United want him to come.
“I think he will, but we might also have to start considering alternatives.”
Simon Moore is the only senior goalkeeper currently on the books at Bramall Lane.
Moore, 29, was the club’s regular stopper before Henderson joined at the beginning of last season.