The 21-year-old forward joined Newcastle from French club Lille in a deadline-day move worth 51 million pounds last month but is still waiting for his first goal.
Fernandez-Pardo missed several opportunities in Monday's 4-1 defeat at Coventry, leaving Newcastle to look for a response when they host Aston Villa on Saturday.
However, Jaissle remains confident that the young Belgian has the quality to make an impact and believes finding the net could give him the confidence he needs.
"Young lads coming into the Premier League for the first time need adaptation time," Jaissle told reporters on Thursday.
He added that he had been advised to give young players at least six months to settle before judging their performances.
"I'm glad that we're seeing Matias in situations where he's bringing the principles on the pitch and creating the chances. It's just the goal missing right now to give him the confidence back," Jaissle said.
The Newcastle boss was particularly impressed with the forward's finishing during training and has no doubts about his potential.
"He's an amazing player, and he has so much potential. We are convinced that it's just a matter of time," he said.
"I have full conviction he will perform again on a good level, and hopefully he will get the rewards."
Newcastle have suffered two heavy 4-1 defeats in their last three matches, with the loss at Coventry following a damaging defeat at Leeds last month.
The results have raised questions about the team's defensive organisation, but Jaissle believes individual errors have been the main problem rather than his tactical approach.
"It's never easy after conceding four goals to talk about the structure and what causes us the problems," he said.
"Against Coventry, we made too many individual mistakes; you cannot talk about formation or technical approach."
The German coach acknowledged that Newcastle's young squad must learn quickly if they are to avoid further setbacks.
"Even though we're a young squad, we need to learn fast," he added.
With Aston Villa visiting St James' Park on Saturday, Newcastle will be looking to respond to their recent defeats.
