Portugal's Jorge Sampaio and Brazil's Luiz Inacio Lula da Silva are also absent, while Venezuela's Hugo Chavez looks likely to remain at home after a car bombing killed a top prosecutor.
While Mr Morales is likely to face tough questions at Thursday's emergency meeting from Brazilian president Brazilian President Luis Inacio Lula da Silva, and his Argentine counterpart Nestor Kirchner, support will come from Venezuelan leader Hugo Chavez.