Manning will reprise her role as Jo Grant opposite Smith in two episodes of spinoff The Sarah Jane Adventures.
"His physicality is one of the most extraordinary things I have seen," she told TV Choice. "I think it's wonderful and so appropriate, so creative with this new Doctor."
She added: "Look at the acts this young boy's had to follow! It isn't easy and I think he has done a miraculous job."
Manning also suggested that her former Who co-star Jon Pertwee would be pleased with her return to the role of Jo.
"He would be thrilled, but he'd be giving us notes!" she joked.
The Sarah Jane Adventures continues this Monday at 5.15pm on the CBBC channel.