McCary, who left the quartet in 2003 due to chronic health problems, was unable to join his bandmates on their 20th anniversary tour.
Band member Wanya Morris revealed that the group would continue as a trio for the live joint, which kicked off earlier this week.
"Unfortunately, it's a situation that we can't actually control - we, as a group, would have loved to put the project together and make it a big event with Mike, but unfortunately we'll have to make it without him," Morris told PA.
"It's the travelling and the tour and with Mike's back and ailments, we will not be able to perform with him so it's hard to have his part there and yet not perform with him."
The group rose to fame in 1991 with debut LP Cooleyhighharmony. Their ninth studio album Love was release in November 2009.
Boyz II Men embark on a three-day 20th anniversary cruise show on February 11.