The France international was set to join the Toffees on deadline day before late interest from Tottenham Hotspur turned his head, and he joined the North London club instead in a £30million move from Newcastle United.
"I thought that was the player for us, what we needed at that moment," Koeman said.
"Then the picture was totally perfect.
"But still, without that player, the picture is very good. I am happy with the squad and the signings."
Koeman signed the likes of Ashley Williams from Swansea City, Yannick Bolasie from Crystal Palace, Maarten Stekelenburg from Fulham and Idrissa Gana Gueye from Aston Villa and Enner Valencia on loan from West Ham United during the transfer window.