Ajax defender Daley Blind is back in full training after collapsing on the pitch in a friendly last month.
On August 25, Blind was taken from the pitch in a match against Hertha Berlin after an alert went off on his implantable cardioverter defibrillator (ICD).
That ICD was installed after the 30-year-old was diagnosed with inflammation of the heart muscle in December 2019 and was forced to miss two months of action.
"Daley Blind's ICD went off," Ten Haag told Ziggo Sport after the match against Hertha. "He got subbed off straight away and he is feeling OK now, he is feeling fine. We will do research about this now."
In a statement on their official website published on Tuesday, Ajax confirmed that Blind had been cleared to return to the pitch following a series of tests.
"Daley Blind is again training fully with Ajax," the statement said. "In the Ajax-Hertha BSC friendly on Tuesday, August 25, the central defender had to be replaced.
"Afterwards, he underwent a few examinations, and as a result he had to drop out of Dutch national team duty.
"The results of the studies gave no reason to keep Blind on the sidelines any longer."
Blind came up through Ajax's youth academy before making his senior debut in 2008, after which he established himself as a regular for his club and the Netherlands national team.
The defender would eventually make a move to Manchester United following the 2014 World Cup, and spent four seasons at Old Trafford.
Blind failed to win the league while at United, but was a part of four trophy triumphs including the Europa League, FA Cup, Carabao Cup and Community Shield.
Blind would eventually make the move back to Ajax ahead of the 2018-19 campaign.
That season would prove hugely successful, as Blind helped Ajax to a domestic double as well as a spot in the Champions League semi-final.
Ajax are set to kick off the 2020-21 Eredivisie season on Sunday when they take on Sparta. The previous campaign was ended early due to the coronavirus pandemic, with no champion declared.