However, the club announced on Tuesday that Roeder was making good progress at the Royal London Hospital in Whitechapel and could be back at Upton Park inside the next two months.
A club statement read: "Tests have revealed a small lesion in the brain that will require neuro-surgery in the near future.
"A full recovery and a return to work is expected within the next six to eight weeks.
"Glenn's wife Faith would like to thank all those who have sent messages of best wishes and support, especially those from many hundreds of Hammers fans.
"Faith has also requested that the family's privacy continues to be respected at this time."