Everton have already spent more than £100m this summer in a bid to take the club to the next level.
However, speaking after Everton's 1-1 draw with Manchester City on Monday night, the Toffees boss confirmed that he is still looking to add new faces to his squad.
Koeman told 'Sky Sports', "we are looking for a left-footed central defender, maybe as back-up for Leighton Baines. With the injury to Funes Mori we don't have any left-footers on that side as a back-up for Leighton. That's an option.
"Also a striker because I think even with the talent of Dominic and Ramirez, look to other squads. They have that number of players. If we need to make the next step we need a striker in as well."