Ten Hag was reportedly interviewed by the Red Devils as their search for their next permanent manager intensifies.
The 52-year-old is currently in charge at Ajax and looks likely to be one of their top contenders for the job, alongside the likes of Mauricio Pochettino.
When asked if he is ready for a big job like United, De Boer - who played alongside Ten Hag for FC Twente during their playing careers - said: "I think yes.
"I think he's had four years at Ajax and has the experience. He had a small club at Go Ahead Eagles and got them to the Eredivisie.
"He then went to Utrecht and was a mid table team and went to Bayern Munich [second team].
"Is he ready and the right moment to move? Yes, he's capable enough and experienced enough to make the step."
Ten Hag worked with Pep Guardiola at Bayern Munich, with the Spaniard currently enjoying huge success at United's rivals Man City.
That's where the Dutchman earned his nickname 'Little Pep', according to De Boer, and it wasn't just about their physical likeness.
He said: "I played with him at Twente and then he went to move as a coach later to Bayern Munich second team.
"He was working a little bit in the shadow of Pep Guardiola at the time. We call him the 'little Pep' as he's so addicted, determined and has a work ethic like crazy for football.
"He analyses and is really technical. He's very into 24 hours to make sure everything is ready for when the game starts.
"In my eyes, he is a very modern coach."
There have been questions over whether Ten Hag could handle the big personalities at a club like United having come from Ajax, who do not have players with the same profile as the Red Devils - including superstar Cristiano Ronaldo.
When asked if he could handle it, De Boer added: "I would say at this moment yes. It is something you have to experience.
"He comes from the east in Holland and they are down to earth. If there is a big guy in front of them, they treat them the same as a small guy.
"They are always treating people the same and I have the feeling he can handle that.
"He's focused in what he wants and everybody has to follow that path.
"At Ajax we also have stars, not to the magnitude you have there, but also big stars.
"He can also put them on the bench and I don't think he's afraid."