Jackson has had to contend with an ever-changing squad in recent months due to ongoing injury issues at senior level seeing some of his players step into the senior ranks.
Leeds are winless in their last 10 PL2 games - a run which dates back to mid-September - though were the far better side against the Toffees as they earned a hard-fought point.
Summer signing Hjelde has been absent since limping off in the first half at Manchester City last month while winger Amari Miller was another missing in York.
Both players, though, are nearing their recovery and will be a welcome boost to the U23s squad.
"They've been out for a little while now," Jackson told the YEP post-match.
"Leo hurt his calf against Man City but he is due to return to training tomorrow [Tuesday]. Amari is the same. He is just nursing a bit of a back injury.
"He had a bit of work done to that so he's on the same timescale as Leo to return anytime. They'll both return to training at some point this week and it'll be a welcome boost to the club as a whole that we're seeing some players come back."
Leeds now have a two-week break over Christmas and into the new year before returning for a clash against Sunderland in the Premier League Cup on January 5.
A trip to West Ham in the PL2 follows just five days later with Hjelde and Miller hopeful of featuring next month.
United made three changes at the break against Everton, a move which saw midfielder Jack Jenkins drop into right-back for a second time at development level.
Asked about the recent test of a new position for the 19-year-old, Jackson said: "Players need to be multi-functional. We know that here. That's just a change where the manager wanted to look at Jack in that position.
"Sometimes it can be disruptive for the team but the boys cope really well with it. They're really effective at adapting and adapting their mindset within the game, because it's not easy to play one position and then switch to another one.
"Sometimes you get a rhythm and a flow to a game in a particular position and a player you're playing up against and then you have to change that into a different area of the pitch.
"It's ever so important in how we play as a club that players can do that. It's just another example of us trying things and helping the players adapt to those positions."