This is the difference between active and passive voice. The sentence is written in passive voice but the English translation has been written in active voice and thus I think some of the confusion. As written it more accurately translates as "This has not been foreseen by the lawyer."
In this particular case, we can tell that "el abogado" is not the object because there's no personal a preceding it. If this has not foreseen the lawyer, the sentence would be, I guess, something like "Esto no lo ha previsto al abogado." Also, I think the context is a fairly big clue: it makes a lot more sense for the layer to be the subject than the object.
You can think of "prever" as pre-"ver" - the conjugations follow those of "ver" which in this case is the irregular "visto." This happens fairly often with verbs that are derived from other verbs that have irregular conjugations (like "conseguir" following the rules for "seguir", or "detener" and "obtener" following rules for "tener" etc.)