Newcastle are keen to offload Mbemba this summer, with Porto looking like the most likely buyers.
The Portuguese club are keen to take the centre-back, but are yet to make an offer that Newcastle feel is acceptable.
Rafael Benitez is looking to sell Mbemba to make room for his own additions, and it seems that he is not prepared to give the Congolese international a chance to force his way back into the team.
The powerful defender has been told to stay at home, while the rest of the Newcastle team are on tour during pre-season.
The Magpies are yet to make any defensive recruits this summer, but they have signed Martin Dubravka and Ki Sung-Yeung, and Kenedy is expected to follow.
Mbemba, who is on a £30,000-a-week contract (Daily Star), has been with Newcastle since 2015, but it seems that he will almost certainly be heading for the exit door this summer.