Uganda Cranes defender is expected to miss the 2021 AFCON Qualifiers double header against South Sudan.
Mugabi will be out for four to six weeks after dislocating his shoulder in the club training, Motherwell has said.
This, comes days after the lanky right back returned to Scotland after the Dubai training camp with the Cranes.
Uganda Cranes will host South Sudan on 12th November 2020 before a second round leg match a few days later.
Born May 1, 1995 in Harrow England, Mugabi made his Cranes debut in a 3-1 friendly win over Sao Tome and Principe.
The former Yeovil player was part of the Cranes team that played at the 2019 AFCON tourney in Egypt.