AFC Wimbledon are set to be without striker Matty Stevens for the start of the season.
Stevens, 28, scored nine goals in 29 League One games before his season was ended in March.
Jackson admitted the Dons need more attacking additions.
“[Matty has] another hamstring problem. So we need to assess him this week to see the extent of it, but probably unlikely to see the start of the season,” Jones said on the club’s website after last Saturday’s 2-0 friendly win over Charlton Athletic at Plough Lane.
“It will probably be a little while into the season until we see him again. It’s probably an area of the pitch that we were looking at anyway, but with Matty being out, it’s probably something we will look at.”
Jackson also provided an update on goalkeeper Nathan Bishop.
He said: “Bish, he hasn’t got a serious one. He was just feeling his thigh after last Saturday’s friendly against Sutton.
“The way he actually pulled out in the warm-up for last Saturday’s friendly, he was feeling something, so we just looked after him. There was no point taking a risk.
“He should be fine at the start of the season.”
Meanwhile, Jackson was pleased with the win against Nathan Jones’ Championship side, but wasn’t getting “carried away”.
“I thought we played really well,” he said. “I thought we deserved to win. They had a couple of chances, especially in the first half in transition.
“I was a bit disappointed with how we gave up the chances, but also really pleased with how we, in the end, reacted and defended it.
“But I thought we moved the ball really well at times, really caused a few issues through our play and through our shape.
“We got a couple of good goals, so for me I’m not going to get carried away. It’s a pre-season game, but to play that well against a team from a division higher, it’s brilliant.”
Wimbledon have made four signings to far this summer. Jackson expects they will do more.
He said: “Yes, there will be. We’re not really close to anything, but we know that we still need to bring in a few more bodies.
“There are areas in our squad that we feel we’re a little bit light and lacking, so we’re working hard on that.
“We’ve still got over a month to go until that window shuts. So we won’t do anything for the sake of it, but we’re definitely looking to add.”
