Could deep vein thrombosis in the leg be caused by a bicycle gash on the leg?

Possible: If it is a very deep gash that has disrupted blood flow it could contribute to a DVT but it is probably not related.

Possible, not likely: Dvt are usually associated with immobility, so if you were immobile after any kind of injury, the risk of DVT would increase. However, i don't think the injury you describe would, in itself, increase the likelihood of this happening.

Not very likely: If the gash was associated with tissue trauma like a crush injury with profound bruising and immobility, then a DVT could be possible, as dr. Press said. But if you only had a cut without much oterh deeper tissue damage, it is unlikely.