The American doctor behind an experimental treatment in the US is to examine Charlie Gard on Monday and Tuesday.
Dr Michio Hirano is due to visit Great Ormond Street Hospital in London, where he will evaluate the 11-month-old's condition.
Hirano is one of the pioneers of nucleoside - an experimental therapy which is being sought by Charlie's parents, Chris Gard and Connie Yates.
Charlie's parents are battling to take their child to the US to receive nucleoside therapy, and Hirano's visit is part of their ongoing battle with Great Ormond Street hospital.
Doctors at Great Ormond Street argue life support should be withdrawn, saying that Charlie's condition - a form of mitochondrial disease which causes progressive muscle weakness and brain damage - would affect his quality of life.
However Charlie's parents believe they - as his parents - should have the final say over his care.