Following Van der Sar's decision to hang up his gloves at the end of last season, Ferguson handed over a fee in the region of £18 million to Atletico Madrid for De Gea.
The 20-year-old stopper won the Europa League and the UEFA Super Cup with Atletico, but has not won a senior cap for Spain - and the suspicion remains that he is yet to be tested at the very highest level.
Now Cech has ramped up the pressure on De Gea by recalling the trouble Ferguson had replacing Peter Schmeichel, who was unconvincingly succeeded by the likes of Massimo Taibi, Fabien Barthez and Roy Carroll.
"It's a huge advantage for Manchester United to have a goalkeeper who is 20 because he can stay for many years," Cech told Sky Sports News.
"It's a huge gamble at the same time because he's joining, historically, a very successful club with great [former] goalkeepers like Peter Schmeichel, Edwin van der Sar, and we all remember how many years it took to replace Peter Schmeichel.
"So let's see what is going to happen now Edwin van der Sar has retired because it's a huge task to fill the boots of Van der Sar."