If it is from a zip-tie as suggested than it can be more than just a flesh wound. Had a friend who caught his leg on a zip-tie while practising CX remounts on his bike and cut through a significant amount of muscle, thankfully he missed his femoral artery by about an inch...
The Tour will be poorer for van Aert's absence. Glad it doesn't sound like a broken leg, being described as a flesh wound.
Let's hope it's not a Monty Python-esque one.