The 26-year-old joined Luton in the summer from HNK Rijeka for a club record fee of £1.3m, and started the first 11 games in the Championship.
However, he made a number of mistakes, before costing Town badly at Derby County, with two clangers in the 2-0 defeat.
He was dropped to the bench and replaced by James Shea, who has kept his place since, but Dearden believes Sluga will take his chance when it comes around again, saying: “Most definitely, he’s a quality goalkeeper.
“He came in and the lads will tell you, the first week we thought, ‘he’s unbelievable.’
“But he went in and made a couple of mistakes, then you try too hard and then it gets to you as you really want to do well.
“In the end he just wanted it too badly.
“His attitude is brilliant, he works hard on the training ground, I think he just wanted it too bad and that maybe tightened him up a little bit.
“So obviously we had to take him out for his own good.
“There is a very good goalkeeper there but we’ve got to get on the training ground, keep working hard, build his confidence up, get him used to the Championship and I’m sure we’ll see the best of him.”
Since dropping out of the team to Shea, Dearden has been impressed by Sluga’s reaction, saying: “James has come in and done well, but Simon has responded really positively.
“He’s trained really well, played for Croatia and getting his second cap, keeping a clean sheet, will do his confidence the world of good.
“I’m sure we will see the best of him, but sometimes it does take a little bit of time to adjust and as we’re all finding out, the Championship is quite a tough league, an unforgiving league, but I’m pretty certain he’ll come back.”
Dearden did admit that Sluga was almost beyond consoling after his mistakes at Pride Park, the first letting Matty Pearson’s backpass slip under his foot and into the net.
He was then beaten at his near post by Tom Lawrence’s cross as Dearden said: “It was really tough.
“In the dressing room afterwards, I tried to speak to him a little bit, but he was so down.
“He’s so desperate to do well, maybe too much.
“He’s really desperate to show people what he can do, maybe’s he’s just trying that bit too hard and it tightened him up.
“He needs to relax a little bit and go with the flow a little bit, he went away to Croatia, that week but when he came back he was still really low.
“I had a chat with him, goalkeeper’s life you’re going to make mistakes.
“Unfortunately for Simon, it’s happened when he’s come over and all in a short space of time.
“But sometimes it happens like that, and the best example is David De Gea.
“Everybody was saying he can never play in the Premier League and now he’s one of the best in the Premier League, so we’ve got no doubt that Simon will come back, but it just takes a little bit of adjusting.”
Sluga would have been an unknown quantity to most Town fans ahead of his summer move, but Dearden confirmed he had a part to play in the Croatian heading to Kenilworth Road.
He said: “We’d all seen him, he played against us when we were in Slovenia two years ago and when we were in Slovenia last year.
“I went and watched him against Dinamo Zagreb, so we’d all looked at him.
“We’d all seen stuff that we really felt would benefit the football club and the club decision was to sign him.”
Being good with his feet was also a key component behind his signing, as Dearden continued: “He likes to play, he’s good with his feet and that was one of the main factors when we were looking to recruit a goalkeeper in the summer, that he has to be good with his feet and he has to want to play.
“Simon is good with his feet, he probably didn’t realise how much pressure he would get with teams pressing, but he’ll adjust.”
When asked what else he thought Sluga had found tougher in England than his native Croatia, Dearden added: “I think it’s a slower game (in Croatia).
“He’s probably less involved as regards crosses, shots, goalmouth action, and especially playing from the back.
“They don’t really press, so there’s a bit more time, and really apart from playing Dinamo Zagreb, a lot of the teams, it’s small ground and small clubs.
“Even coming to Kenilworth Road with 10,000 in, a full stadium and then you go to places like Derby and Middlesbrough and all those places we go to, it’s a big change, but he’s an international goalkeeper and he will adapt.
“He’s obviously progressed through Croatian football and international football.
“So all the signs are there that he will adapt, but maybe it will just take a bit more time here.”