فِي خُسْرٍ

فِي خُسْرٍ is a phrase (شِبْهُ الجُمْلَةِ) consisting of a particle of pulling down (a preposition) and a genitive noun

PhraseParticle / NounNoun Particle
شِبْهُ الجُمْلَةِجَارٌ وَمَجْرُوْرٌاسْمٌ مَجْرُوْرٌحَرْفُ جَرٍّ
PhraseCompoundGenitive NounParticle of pulling down
  
in lossفِي خُسْرٍ=خُسْرٍ+فِي
in losslossin
Surah/Below is the only verse in the holy Quran containing the preposition and genitive noun compoundفِي خُسْرٍ
Verse
103-2Surely man is in certain lossإِنَّ الإِنْسَانَ لَفِي خُسْرٍ