Strained Leg Muscle advice?

Based off a diagram I believe it's the peroneus longus. I've been pushing myself somewhat hard on split exercises, since I'm almost all the way to the ground on both sides and I started four days ago. The third day felt fine with the usual feeling of tension in my legs. But today as I did my warm ups getting ready to go again I felt a really strange tension/discomfort running a line down the center of the back of my lower leg, only on the left side. Uh... should I be worried? I mean, I'm guessing that leg wants a break, but did something bad happen? It doesn't spasm until I start doing split warm ups.