Zakat is to be paid on the loan that was given to others if it meets the conditions of zakat. Not having that money in possession does not mean that it isn't liable to pay Zakat . The obligation of paying Zakat is applicable to the lender if he is a well-off person and able to pay it off at any time.

Zakat is due on the lender every year even if he does not collect his money as this is akin to possessing the money but at the safekeeping of another.

However, if the debt is unlikely to be collected then Zakat is due upon collecting it as this is the position of Shafi`i scholars and is the stricter opinion. Nevertheless , Hanafi scholars are of the opinion that zakat is due on such a loan for a haul (one lunar year) when the lender regains its possession and this is more facilitating.