Juventus head coach Maurizio Sarri thinks "something has changed" mentally for Gonzalo Higuain since his difficult loan spell with Chelsea.
Higuain joined the Blues on loan in January but could not offer consistent form in front of goal, scoring just five times in 18 appearances in all competitions.
The striker's long-term future at Juve seemed to be in doubt when Sarri took charge in Turin, but the Argentina international has looked rejuvenated in the early months of the season.
The 31-year-old has managed a modest three goals in 11 appearances but has generally performed well alongside Cristiano Ronaldo or Paulo Dybala in attack.
Sarri thinks there has been a significant change in Higuain's mentality since a worrying moment during his final few months in charge of Chelsea.
"Gonzalo is a great player who had spent a difficult season," Sarri said of the former Napoli forward, who is expected to have recovered from a head injury in time to face Torino on Saturday.
"This summer, I saw him train with an exceptional level of motivation. In London, I had heard some comments by him that I hadn't liked at all, but now it's all to the contrary, which meant something had changed in his mind. And when he has high motivation, he is a very important player."
Sarri, who is unsure whether midfielder Aaron Ramsey will be fit for the derby, watched his side stay a point clear at the top of the table thanks to a 2-1 win over Genoa on Wednesday.
Ronaldo scored the winner from the penalty spot in the 96th minute having seen an earlier goal disallowed for offside following a VAR review.
There was greater controversy in Napoli's 2-2 draw with Atalanta, when the visitors' 86th-minute equaliser at the San Paolo was allowed to stand after VAR decided not to award a penalty to the home side.
Head coach Carlo Ancelotti was sent off for his protests and Sarri admits he is also not a fan of the way the technology is being used in Italy.
"I've honestly never thought or spoken about it very much. I prefer it when referees make their own decisions on the pitch. This is a strictly personal opinion," he said.
"Rules are different now and not all of them are agreeable, including, for instance, the latest specifics on handball, about which, to be honest, despite trying to read many times, I don't much understand.
"We have to comply with these rules. Even in everyday life, there are many rules I consider absurd, but I can't make myself go to prison by violating them. These are rules we have to respect.
"If you ask me if I like it, I'd say no. It was brought in to right macroscopic wrongs, but if you need VAR four times per game, I guess it's impossible to make four big mistakes per match. In the rest of Europe, VAR usage is much more limited."