United States global Pulisic will return to Dortmund on loan before completing his move to Chelsea in the close-season.
The Italian was asked about the Pulisic's signing after Wednesday's draw against Southampton at Stamford Bridge.
"I didn't know anything about Christian Pulisic yesterday", Sarri said.
"My opinion was positive and today I've known that the deal is done but I didn't know anything. I can only say my opinion to the club".
He said: "I think it is easier for me because I know how he [Sarri] works and I know what he wants from me on the pitch".
Paris Saint-Germain are claimed to be keen on signing the midfielder and some of the top names in the Premier League are also very much interested in getting their hands on him. I have to try to improve my players, my team, my offensive phase, or better my offensive phase in the last 20 metres.
Due to this, there has been a general dependency on Hazard to produce the goods but he has still not managed to standout in every game which has partly contributed to the Blues' fourth position in the standings.
The Blues have been in dire need for an attack-minded player who will inspire the club's frontline since the start of the season, they finally have a very youngster capable of wreaking havoc to any defence next season.
"The problem is today it was important to change the match and it was impossible".
Chelsea will not be signing AC Milan striker Gonzalo Higuain during the January transfer window, with the complexities of the deal making it not viable for the Blues.
But the winger who had been linked to Liverpool will be loaned back to the Bundesliga side until the end of the ongoing League season in Europe.