The former world number one has surprised many, including Rusedski, with the level at which he has been able to play only eight and a half months after hip resurfacing surgery.
In a three-week stint in China, Murray beat now world number 11 Matteo Berrettini and pushed Dominic Thiem and Fabio Fognini hard in close defeats.
It was a big step up from the performances Murray produced on his return to singles action in America in August and gave hope to his fans, as well as the Scot, that he could perhaps again challenge for tennis' biggest titles.
But, after two years of struggles with his right hip and at the age of 32, Rusedski believes it is too early to make future predictions.
The former British number one told the PA News Agency: "I've been pleasantly surprised. I thought it would be much more difficult for him, I thought it would take a little bit longer, but he's played very, very well.
"The question mark is still how much can his body take week in, week out. There's still a long road back.
"He's played two matches back to back, but can he play three, four, five days in a row? It's too hard to predict. I think we'll know more when he plays the Australian Open and a three-out-of-five-set match.
"It's not his mentality or his tennis, it's what the body will allow him to do. But the signs are very positive."
Rusedski and Murray are on a list that now includes Dan Evans, who at 43 in the world is the top-ranked player in Britain for the first time.
Evans' stellar form since returning unranked from a year-long drugs ban last spring coupled with Kyle Edmund's slide has left the 29-year-old in top spot, and Rusedski believes he can climb significantly higher.
"Sometimes you go through difficult situations and it forces you to grow up and take stock and do all those things that Dan has done," said Rusedski.
"We've always known he had the talent and the ability and I had a feeling at the beginning of this year when I saw him in Australia that he was going to have a fantastic season.
"I think top 20 would be a realistic goal for him if he can keep on the momentum he's had this season."