Pedro was brought down in second-half injury time on Thursday, and appeared to have dislocated his shoulder as he left the field.
The 31-year-old has had a productive start to the season, scoring three goals in his first seven matches for the in-form Blues.
Although the Chelsea manager admits he is unsure on the details of the Spain international's injury, he does not expect it to be severe.
"The problem is his shoulder, but I don't know exactly the situation," he told reporters after the game. "I've spoken with the doctor, but only for a few seconds. The doctor told me that probably it's not a very serious injury."
Willian's first-half strike proved the decisive moment in the game as the London side opened their Europa League campaign with a victory in Greece.
And although Sarri saw his side as the dominant team, he was disappointed that they did not score more.
"I think we were in control of the match for 90 minutes," he said. "We had a lot of opportunities. So I am really very happy with the three points, very happy with the performance I think, but I am not very happy with the result. When it is time to kill the match, we have to kill the match.
"I think we played very well. We were in control of the match. It was difficult for everybody to play against us this evening. I hope we were so good and it's not PAOK's fault.
"I have seen five or six matches of PAOK and I think there are very good players," he added. "For example the number 10, Dimitris Pelkas, I think he is a very good player. Maybe not in this match. But they have some good players."