I damaged my abductor last year on a tough climb, and have never really gotten over it.
Thinking back, there were warning signs that it was weakening, as on longer rides I could feel a swelling at the very top of my leg and I could feel the strength in that leg seeping away. Months of rest and physio failed to help much and any improvement was painfully slow. The pain soon radiated to my hip and groin with no sign of improvement. I had a couple of false dawns when I tried to get back on the bike, only to breakdown again until I went to visit a massage therapist. This girl is brilliant, but she wasn't available so I went to see her husband and I thought he was even better when dealing with deep tissue as you need the strength to make an impact. I did an over night 40 miler for the summer solstice and it was great to feel back to full strength but it started going back the way again soon after, so I need to get back.
As for stretching, I'm rubbish at it, but it is a very difficult area to stretch, so I'm looking forward to seeing suggestions here.