The 72-year-old music icon was hospitalised in Tokyo, Japan, for six nights due to a virus in May, reported Contactmusic.
"I spoke to him while he was in hospital. He said he was doing OK. Now he is getting fit and getting ready to rock," Starr said.
McCartney was forced to cancel several concerts in Asia after falling sick, but he is now recuperating and on holiday in Ibiza with his wife Nancy Shevell, 53.