The 24-year old Honduran midfielder is a free agent after departing Deportivo Vida and has been impressive during training with 'Gers according to McCoist.
"We are close now with Arnold," said McCoist.
"We watched him playing for Honduras against Panama and he did well. Terms have been agreed with Arnold so hopefully in the next three or four days we'll push that one through.
"Arnold is very aggressive and gets about the park well so I think he would blend in with the rest of the midfield and be a good signing."