The announcement made this morning on the club's website is in direct contrast with manager Eddie Howe's statement at the weekend, when he claimed the Swede would "absolutely" be travelling to Singapore and South Korea.
That was after Isak played no part in Newcastle's 4-0 friendly loss to Celtic, while the forward has been training alone in recent days.
The reason given for Isak's absence on the tour is a minor thigh injury. However, the announcement is likely to fuel speculation that the 25-year-old is close to sealing a transfer away from St James' Park.
Liverpool have been the frontrunners for the striker's signature over the summer, taking over from Arsenal, who are now close to completing a move for Isak's compatriot, Viktor Gyokeres.
Newcastle will face the Gunners in Singapore, before heading to South Korea to play a K-League All-Star team and Tottenham Hotspur.
The Reds are said to be willing to part with the Magpies' £120 million asking price, though they are also facing competition from Saudi Arabian club Al Hilal.