Djokovic, speaking to reporters as he prepared to defend his US Open title, said players who have bemoaned a lack of transparency in the Sinner case make a valid point.
"I understand the frustration of the players is there because of lack of consistency," the 24-time Grand Slam champion said.
"As I understood, his case was cleared the moment basically it was announced. But, you know, I think five or six months passed since the news (of the positive tests) was brought to him and his team.
"So, yeah, there is a lot of issues in the system," Djokovic said. "We see lack of standardized and clear protocols. I can understand the sentiments of a lot of players that are questioning whether they are treated the same."
Several players have suggested Sinner received special treatment because of his ranking, asking why he was not provisionally suspended as the investigation that exonerated him played out.
Sinner insisted on Friday that he was treated the same as any other player.
"There is no shortcut, there is no different treatment, they are all the same process," Sinner said.
The Italian was notified earlier this year he had tested positive for low levels of the banned anabolic agent clostebol during the Indian Wells Masters in March.
An out-of-competition test eight days later was also positive.
Sinner said he was, in fact, provisionally suspended for several days, although that fact was not made public at the time.
But he and his camp quickly appealed on grounds the drug entered his system when his physiotherapist used a spray containing it to treat a cut, then provided massage and sports therapy to the player.
He was allowed to continue playing as investigators studied the case, with the International Tennis Integrity Agency announcing on Tuesday he had been cleared of wrongdoing.
He said he had fired physio Giacomo Naldi and trainer Umberto Ferrara -- who supplied Naldi with the spray -- citing a loss of confidence in them.
World number three Carlos Alcaraz, indicated Saturday he thought there was more to the case than had been made public, but he declined to criticize the ITIA decision.