The versatile defender has rejoined the club he left to move to United four years ago, after helping the Reds win more silverware in his time in Manchester.
“I would like to say a big thank you to Daley Blind for everything he has done for the club since he joined in 2014,” the boss told ManUtd.com.
“I have to say, that in my 18 years of management, Daley is the one of the most professional players, both on and off the pitch, that I have had the pleasure to work with.
“I would like to take this opportunity to wish him all the very best as he rejoins his boyhood club, Ajax, and thank him for from the bottom of my heart for his commitment and dedication over the past four seasons.