Pedro was involved in an accidental collision with PAOK goalkeeper Alexandros Paschalakis in the final minutes of the Europa League Group L fixture and was helped from the field by Chelsea medical staff.
Sarri confirmed the Spaniard needed to be further assessed to determine the severity of the injury but said his initial impression was that it would not prove as damaging as first feared.
"I don't know exactly the situation," the Italian told a news conference. "I have only talked to the doctor for a few seconds and he said probably it is not a very serious injury."
Chelsea picked up their sixth consecutive win in Thessaloniki courtesy of an early goal from Willian, but Sarri was disappointed that striker Alvaro Morata failed to make the most of his return to the starting lineup.
Morata has lost his place to Frenchman Olivier Giroud and Sarri admitted the Spaniard was in severe need of confidence boost to rediscover his touch in front of goal for the Premier League leaders.
"Alvaro has to gain confidence with one, two, three goals," Sarri added. "I am not able to give him confidence. In this match, he had three or four opportunities.
"He was unlucky. I hope for him in the future I can help him. But the confidence can come with goals. For the first time in this season, he was ready in the box. He was on the ball and was active."
Chelsea visit London rivals West Ham United in the Premier League on Sunday.