Morelos, 24, has been a revelation in Scotland since he joined Rangers from Finnish side HJK in 2017.
The Colombian international has netted 77 goals in a total of 137 games for the team coached by Steven Gerrard.
In the 2019-20 season, Morelos scored 29 goals and contributed 11 assists.
RMC reports that while personal terms have been sorted, the two clubs must now agree a fee.
However, everything seems to point to LOSC finally landing their Osimhen replacement in the form of Morelos.