I'll name 5.
Left back, Right back, Central defence considering Jan and Toby are playing out contracts. Midfield, and up front considering Kane has had no real competition for years.
You could arguably add the goalkeeping position to that scenario as we're fucked without Hugo too.
Left back - Sess (25m) brought in with Davies and Rose, both international players.
Right back - Fair enough
Centre back - Foyth and Sanchez (42m) brought in to cover for Toby and Jan.
Yes, massively under-invested.