Not intending to raise unnecessary worry, VT:
"Methotrexate may cause serious or life-threatening skin reactions. If you experience any of the following symptoms, call your doctor immediately: fever, rash, blisters, or peeling skin." I found it at this NIH web site:
http://www.nlm.nih.gov/medlineplus/druginfo/meds/a682019.html
It's the 9th paragraph.

Generally speaking it can happen that abrasion increases the severity of any kind of skin reaction that would normally be mild. But maybe still worth having checked out.