The 20-year-old centre-back was due to play in Sunday’s international friendly against Iceland in Carson, California, but left the US camp in midweek to travel to England to complete a £3.5 million move to Stamford Bridge.
Having only been a full-time starter in MLS for one season, the youngster is facing plenty of questions over whether he can make the grade in the Premier League, but his national team boss has praised him for taking the plunge and challenging himself at the highest level.
"It's a huge move for [Miazga]. Being 20 years of age, and now getting the opportunity to go overseas, and proving himself, is big," said Klinsmann, who handed Miazga his senior international debut in November’s opening World Cup qualifier against Saint Vincent and the Grenadines.
"It's big I think for our program, it's big for us when a player moves to a Champions League team, a big team, a big club. We are happy for him, we are pleased, but we know also he is just developing.
"It's courageous from Matt. It's a big opportunity, no doubt about it, so we are thrilled for him."
Miazga originally joined the Red Bulls academy in 2009 before signing a Homegrown Player contract with the MLS club in 2013 after rising through the development ranks.
The New Jersey native, who holds a Polish passport by way of his parents, featured just eight times for the team during his first two seasons in the US top-flight but saw his reputation soar during a breakout 2015 campaign, as he established himself as a regular starter and proved instrumental in helping Jesse Marsch’s side win the Supporters’ Shield title.
His displays earned him his one and only senior US cap so far in November after previously starring at the Under-20 World Cup last summer, when Chelsea are first reported to have taken an interest in him [h/t FourFourTwo], while he was also named the US Soccer Young Male Player of the Year in December.
The burning question now is how much first-team action he will see at Stamford Bridge in the immediate future, with most expecting him to be loaned out at some stage given his lack of experience at the top level of the game.
Manager Guus Hiddink has indicated that the 6ft 3in stopper will remain with the senior squad for the rest of the season before a decision is made in the summer over what would be best for his development, and Klinsmann seems to be in favour of that approach.
"In the long run, [Miazga] is a player that we're going to count on," Klinsmann told ESPN FC. "He has showed already a lot of potential over the last two years, not only with [the U.S.] programs but with the Red Bulls, and now this is a big, big step.
"But we've got to be patient there. It will take time. He will go there to learn, and it will take time until he gets his chances there."