The 20-year-old has been with the club for the last 13 years, and has appeared in 17 Championship fixtures during the 2017-18 campaign.
"Dael is an up-and-coming player who we're enjoying working with," Boro manager 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."
Middlesbrough, who have won three of their last four in the Championship, will look to cement their spot in the playoffs when they host Millwall in the second tier this weekend.