Greatorex, 20, has joined the Gladiators on a month’s loan from Championship club Barnsley.
He goes straight in to the team for their Integro League Cup tie at Worksop.
Matlock say they are unsure how long Stewart will be sidelined, and haven’t revealed details of the injury sustained on Monday.
Greatorex has been at Barnsley since the age of seven and has also been on loan in the NCEL with Penistone Church.
Keep up-to-date with our exclusive email newsletters.
Subscribe