If a witness gave a statement but have not sworn to it and become unavailable on his own will but the prosecution apply for a application implying

Presumably any experienced criminal defense attorney already knows the procedure for filing a motion in limine, or, in the alternative, for making the appropriate objection at trial.  The defendant's constitutional right to confrontation of a witness is normally the primary aid to the defense attorney in such a situation.  However, there may be other objections -- depending on what the testimony is -- and the purpose for what the opposing side is trying to use the statement/s.  There are hearsay objections that often can be asserted.  However, there also are exceptions to hearsay.  So, again, it depends on what is being asserted and for what purpose -- and whether the witness is determined, by the court, to be unavailable. Even if a determination of unavailability is rendered by the court, that does not resolve the issue of confrontation.  However, as noted in the first sentence, any experienced criminal defense attorney already knows this.  So you should not be need to be concerned about trying to instruct the attorney.