Malcom has struggled since joining the Catalan giants, which has in turn affected his game time and the 21-year-old winger is also supposedly looking for a move away from Barcelona.
Willian has been strongly linked with a move to the La Liga champions in recent days. Barcelona then went ahead with Malcom.
Willian to Barca in cash-plus-player deal?
Barca have reportedly made a renewed approach, with Malcom thrown into the deal, which Chelsea are also thought to have refused.
The Blues have shown glimpses of becoming an exciting attacking team, but Sarri is still trying to fit the pieces together following his summer arrival at Stamford Bridge.
Sarri's wing options have been bolstered by the return to fitness of both Willian and Pedro from muscle injuries, but uncertainty surrounding Callum Hudson-Odoi's future makes Willian's availability all the more important.
Willian had been subject of a transfersoap during the pre-season, with FC Barcelona reportedly interested to sign the winger. "I think he can do better, because the potential is higher, but he's very important for us, so I think it's impossible to lose him in January. I don't know what you're talking about".
"Usually he wants ball on the feet, so I think he can improve in movements without the ball", Sarri said. "He has the potential to score more".