During the game against the German side, the Dutchman fell to the floor with nobody around him, with Ajax players subsequently sprinting to his aid.
He did manage to walk off the pitch after initially falling, but it presented a terrifying moment for the player and those in attendance.
After feeling dizzy in a Champions League fixture against Valencia in 2019, Blind was diagnosed with inflammation of the heart muscle.
For those asking, out of nowhere, Daley Blind again collapsed to the ground out of nowhere, and a loud scream followed. He was able to walk away from the pitch afterwards. But God, this is so freaking terrifying.— 𝐀𝐅𝐂 𝐀𝐉𝐀𝐗 💎 (@TheEuropeanLad) August 25, 2020
He was then fitted with an implantable cardioverter defibrillator (ICD), which went off during the game against Hertha, as confirmed by Ajax head coach Erik ten Haag.
"Daley Blind's ICD went off," Ten Haag told Ziggo Sport.
"He got subbed off straight away and he is feeling OK now, he is feeling fine. We will do research about this now."
Blind faces another period out of action as doctors ascertain when it will be safe for him to return.