The American claimed her 19th title at the Australian Open on Saturday, tying her with Helen Wills Moody and moving her just three behind Graff and a further two off the mark set by all-time leader Margert Court.
The 33-year-old Williams is still fit and firing, and while she remains at this level, Mouratoglou believes that Graff's record is within reach.
“Of course she can,” Mouratoglou said of breaking the record.
“I'm not saying it's going to be easy. For sure it's going to be very difficult. She will have to stay fit, she will have to keep the motivation as high as it is now. She has been playing 17 years on tour, so to wake up every morning, go to practice, all these things.
“But she still has for the moment.”