Although he was putting in plenty of work in training camps and in the lead-in to a fight, Parker developed a tendency to switch off during bouts.
It was the main area of concern for new trainer and former WBO middleweight champion Andy Lee, who has worked to get Parker back into the world heavyweight title conversation — with Sunday's clash against Derek Chisora in Manchester the first major step in the journey.
Parker joined Lee at the start of the camp after parting ways with long-time coach Kevin Barry following a unanimous decision win over Junior Fa in February. Lee came recommended to Parker by WBC heavyweight champion Tyson Fury, his second cousin, and told the Herald he had to go back to the basics with Parker to break him out of bad habits.
"He would have momentary lapses in concentration for a round, where he would look to take a break. That's down to laziness and it's just a bad habit. He would do something really good, then take a little walk and switch off, and he'd allow his opponent opportunities to come back into the fight or the round," Lee explained.
"At the top level you can't do that; you have to be focused for every second of the round. It's only three minutes, but it's mentally fatiguing to do that. To be that focused and concentrate, it's mentally draining as much as is it physically draining, boxing. So, you have to train that side of things as much as the physical, and we have been doing that," said Lee.
"First, you have to make him aware of it, because he wasn't even aware of it. On the pads, little tells, little ticks and I would say 'hey, that's a break' and he would kind of recognise them himself, but for a round he might have done that two or three times. He started to minimise that. It increasingly got less and less.
"Then in sparring, again, we had to start from the basics, because sparring is a different situation. So, we had to start from the bottom and keep reminding him.
"Now he can recognise it himself and he agrees — he has to stay focused; the best fighters stay focused all the time," said Lee.
"I don't like criticising him too much because he was a world champion before we started training together. Kevin Barry did a fantastic job; Kevin Barry and him became world champion together.
"Kevin Barry is a lot more experienced than me and has done more in the game than I have.
"But I believe I have improved Joseph, and I think he would agree with that."
Lapses in concentration are of concern against an opponent with the style of Chisora, who likes to dictate the pace, fight on the front foot and throw heavy hands throughout.
Although Chisora has stumbled against the likes of Fury, Dillian Whyte and Oleksandr Usyk, he is a proven punisher when his opponents aren't fully focused for the full fight. Lee pointed to his win over Carlos Takam, an eighth-round TKO, as a prime example.
"Takam was winning that fight, then one lapse in concentration and he got knocked out. Chisora will always have that threat, so Joseph knows he has to be switched on completely for the whole fight," added Lee.
Although Parker comes into the bout on the back of three straight wins, it shapes as important in the context of his career.
Chisora has become something of a gatekeeper in the heavyweight division and with 23 knockouts in 32 wins, he has shown he has the ability to win a fight in a number of ways despite his knockout-friendly style.
Lee spoke to Fury about how Parker's training was progressing ahead of the bout, and said Fury summed up the Kiwi nicely.
"Tyson just said, and Joseph heard the message, 'if he's any good he's going to beat Chisora. If he can't beat Chisora, he may as well forget about it' and that's the truth," Lee said. "Joe knows that; he has to beat this guy. Chisora is a very good heavyweight, he won't beat maybe the top three guys in the world but he'll beat a lot of the rest of them; he carries a threat and one lapse you're going to get knocked out.
"But Joseph's youth, speed, his boxing IQ — he shouldn't be losing this fight. He knows that, and if he's any good he's going to beat this guy.
"We live and die by our results in this sport; it's the results that matter. We have done everything right, we've trained extremely hard," said Lee.
"But if Joe doesn't win this fight then, probably, I'll get blamed for it or he'll get blamed for it and no one will want to hear anything else."