Royal College of Nursing (RCN) general secretary Pat Cullen said she had a "chink of optimism" after noticing a "little shift" in the Prime Minister’s stance on Sunday.
The Prime Minister also refused to say whether he uses private healthcare as Britons struggle with long waiting lists to see GPs and receive treatment.
Ahead of talks with the union on Monday, Mr Sunak insisted pay demands would be at the forefront of talks.
Speaking BBC’s Sunday With Laura Kuenssberg programme the Prime Minister said Monday’s talks are "really important" and that “the most important thing is that we are talking.”
"When it comes to pay we’ve always said we want to talk about things that are reasonable, that are affordable and responsible for the country," Mr Sunak said.
"We are about to start a new pay settlement round for this year, we’re about to start that independent process, and before that process starts the Government is keen to sit down with the unions and talk about pay and make sure they understand where we’re coming from."
The Royal College of Nursing (RCN) has called for discussion to not only focus on pay for 2023/24, but also the current financial year.
Unless a breakthrough is made, nurses will strike in England on January 18 and 19.
In response to Mr Sunak’s comments, the general secretary of the RCN, Pat Cullen said: “Then I listened to that there was a chink of optimism and there was a little shift in what the Prime Minister was saying."
However, she added of his comments: "This is not about negotiations tomorrow, it’s not about nurses’ pay and it’s not addressing the issues that are our dispute and that is addressing pay in 2022/23."