The 20-year-old, a member of England Under-20s’ World Cup-winning squad, has made 17 first-team appearances for Boro this season.
“Dael is an up-and-coming player who we’re enjoying working with,” Boro boss Tony Pulis told the club’s official website.
“He’s had a taste of the first team and he’s been in and around the squad. He knows he has a lot of hard work ahead, but this is a good opportunity for him.
“He’s a Middlesbrough lad as well, having come through our academy, and he’s a great example to other young players coming through here.”
Fry made his league debut for Boro in August 2015 at Preston and has made a total of 27 appearances for the club. He featured 10 times for Rotherham during a loan spell in 2016.