A pensioner fighting for life in hospital is not expected to walk again after being dragged 20 metres by a train at Heatherdale station in Melbourne's east.

Lilydale father John Roberts, 57, was trying to board a train on Saturday afternoon when he became trapped in the doors.

"I haven't seen the CCTV yet, but I got a report from the hospital saying that he got caught in the doors and dragged about 20 metres and he got slammed into the platform wall," his brother Paul told The Age.

"Then he fell down, and his leg went down between the train and the platform."