They have now made some changes in the squad, but are yet to secure a mega transfer during the summer 2026 transfer window. Also Read: Top nine clubs with most goals in FIFA World Cup 2026Most expensive transfers of summer 2026S.No Player From To Fee 1. Marc CucurellaMarc Cucurella (24) won the FIFA World Cup 2026 with Spain. This makes him the most expensive signing of the summer 2026 transfer window. Who is the most expensive signing of the summer 2026 transfer window?