The Whites fell to a 3-1 defeat to Leicester City in Premier League 2 action on Friday night in York - a result which saw them extend their winless run to nine games as they dropped into the bottom two relegation places.
Joffy, as he is affectionately known, gave Jackson's men a deserved lead in the opening exchanges though the game turned following a Charlie Cresswell red card.
The Leeds skipper received his marching orders for a second bookable offence on 32 minutes for dragging down Tawanda Maswanhise on halfway.
His dismissal altered proceedings as the Foxes went on to score twice through Ethan Fitzhugh before Bayli Spencer-Adams sealed the three points with a diving header.
Gelhardt took a heavy knock ahead of the half-time interval and failed to reappear for the second half, being replaced by midfielder Jack Jenkins.
Jackson, though, says the sub was a precautionary move due to a dead leg with Leeds not wanting to take any risks.
"Joffy [Joe Gelhardt] was going to do 90 minutes today, it's a little bit of a precaution with him with the dead leg he got, we didn't want to take a real risk with him," the Whites development boss said post-match.
"He was down for a much-needed 90 minutes today but unfortunately he got that knock which was hindering his movement a little bit so we didn't want to take any chances which is a sensible thing to do."
Asked about Cresswell's red card which came in his first outing as a defensive midfielder, he said: "I think probably both challenges warranted a yellow card to be honest.
"You've got to be experienced in that position. Charlie assures me he didn't realise he got one [a yellow] early on in the game because he didn't see the referee show him the card, but he did and we have to learn from that. We have to live with that.
"Ultimately the red card has cost us. Up until the sending off everything we spoke about with the players and highlighted before the game was working to good effect.
"Listen, mistakes happen in football. We just need to know how to deal with games and combat those situations."