Manchester City's Eliaquim Mangala in action against Arsenal's Alexis Sanchez
With Everton eager to make further defensive additions before the end of the transfer window following John Stones' big money move to Manchester City, the Toffees should perhaps consider making a move for a defender who is out of favour at the Etihad.
The Goodison Park arrival of Sunderland's Lamina Kone has failed to materialise, and with the club considering other options, Eliaquim Mangala could be a signing that could benefit the Toffees under Koeman.
The French international is said to be nearing the exit door at Manchester City, but with the majority of reports indicating interest from the likes of Valencia, who may be looking for a defender to replace Arsenal target Shkodran Mustafi, is there a case for him staying in the Premier League?
Manchester City's John Stones in action with Sunderland's Lynden Gooch
Mangala hasn't been involved in either of the Citizens' first two matches of the season, with Aleksandar Kolarov and then Nicolas Otamendi partnering Stones. With the 25-year-old not even making the bench despite Vincent Kompany's absence, it is clear that Pep Guardiola doesn't feel the former Porto man is up to the job.
But if the Toffees can recruit a player that City spent over £40 million on according to the Manchester Evening News, for a portion of that price, they have the perfect manager at the helm to bring the best out in him.
Everton manager Ronaldo Koeman
Though Mangala's first season at the Etihad was a struggle, he showed signs of improving last year, and if anyone can nurture his quality it is former Barcelona star Koeman, who was one of the top centre backs in the world in his playing days.
Both Ashley Williams and Yannick Bolasie referenced this fact about the Dutchman, proving that he isn't just a major draw for players, but also possesses the experience and knowledge to get the best out of players.
Koeman would certainly be able to improve Mangala, or indeed any defender on his positioning, communication and concentration.
At his two years at Southampton Koeman ensured the Saints boasted one of the best defences in the division, with the Saints actually conceding the same number of goals as City and finishing just three points short of the Champions League places.
Everton manager Ronald Koeman (L)