The Whites January addition made his first competitive bow for the club on Monday night in the development ranks.
Joseph was a substitute in a Premier League 2 defeat against Blackburn Rovers, stepping off the bench in the final 10 minutes in a 4-0 defeat across the Pennines.
The 18-year-old is a player Leeds are quietly excited about but know he will require patience as he settles into life in England.
Victor Orta and his scouting network extensively researched the former Espanyol forward before bringing him into the club earlier this month, having beaten away interest from the likes of Catalan giants Barcelona.
It was at the Lancashire FA, though, where supporters got a glimpse of what ability he possesses after a whirlwind few weeks of getting up to speed.
"I put him on tonight [vs Blackburn] to give him a taste of it and get him a run out," Jackson told the YEP post-match.
"He's been working hard behind the scenes. He's had to work on his physical development and integration into the group. He's doing that slowly but surely. It was nice for him to get on the pitch, albeit probably not in the circumstances he would've wanted to come on in.
"He's integrated okay so far. We'll continue that progression of him in getting used to how we play while he gets better and fitter."
Jackson has been working behind closed doors with the striker at Thorp Arch in recent days, helping him learn the Leeds way after a period of training on his own before signing on the dotted line in West Yorkshire.
As first impressions go, it has been a strong one - along with 44 goals in 56 games across three seasons in Espanyol's youth system.
"He's got good physical attributes, his finishing is very good," Jackson added.
"We've seen him in a few finishing drills and a few other drills that we work on, so he looks like he can finish as well. His movement's good and, like I said, we're just getting to know each other at the minute - he's getting to know his teammates, he's getting to know the club, but everything's going along nicely.
"We fully expect him to integrate into the group - he's eligible for the 18s as well, so if that means him getting game time down with them, when their games come about again, then we'll maybe utilise that but he'll be working with the 23s group predominantly and he'll continue his integration there."