As early as the late-1980s rumours were abound that Israel had sold Lavi's design to China, which the Israelis denied. It's possible that Israel provided the airframe design and data on certain avionics and aerodynamics but question remains how much of an information and assistance could it have provided, especially on the items of U.S. origin? In any case, except for the basic airframe design influence the J-10 has emerged as a completely different aircraft. Israel is, however, unlikely to protest the Chinese sales of J-10, even if the rumours are true, for two reasons:
1. Israel simply cannot influence Chinese decisions
2. Despite its hawkish stance against Israel, Pakistan does not threaten Israeli security