Giorgio Chiellini's absence through injury and fitness issues has been one of the "great regrets" for Juventus coach Maurizio Sarri this season.
Chiellini, 35, ruptured a knee ligament in August, ruling him out of action until February, when he made a couple of Serie A appearances before the league was suspended due to coronavirus.
The centre-back still has not featured since the resumption last month because of fitness-related issues, though he was given a new one-year contract to keep him at the club until 2021.
Sarri confirmed Chiellini has been in full training over the past week and is still considered an important player.
Speaking ahead of Wednesday's trip to Sassuolo, Sarri said: "Chiellini's absence is one of the great regrets of this season.
"He is a player who knows how to be enthralling. He has been training with the team for five days. I see him growing, and, in the future, he will give a great contribution for us."
The centre of defence is causing Sarri regular headaches at the moment, with Merih Demiral still recovering from his cruciate ligament rupture, while Leonardo Bonucci is a doubt for Wednesday's match.
"Merih Demiral is fine, but he needs time to get back into physical form," he said, before adding: "Bonucci has a problem with his foot that we need to evaluate today [Tuesday]."
Despite dropping points in each of their past two league matches, Juve remain in charge at the Serie A summit with an eight-point lead over Inter and Lazio.
But Sarri is not expecting a straightforward contest at Sassuolo, who are making a late push for the European places after going unbeaten in six and winning each of their past four games.
"Sassuolo is a team that is on the same path as Atalanta," Sarri continued. "They are giving continuity to a project, they are organised, and with a smart coach.
"They are in excellent form and are a dangerous team. The team has scored 17 goals in six games, so they don't have a problem when it comes to scoring.
"[Roberto] De Zerbi always manages to make an impression on his teams. He is the most interesting of the young coaches.
"We will be at least equal on the level of enthusiasm and determination, because we are in a moment where we are playing for the Scudetto."