Koeman has made it clear that he will opt for a hybrid 4-2-3-1 formation to get the best out of the squad available to him, particularly in the attacking positions.
With Marc-Andre Ter Stegen out injured for another month yet, Neto will play in goal, and with Nelson Semedo sold to Wolves, Sergi Roberto is the only recognised right-back in the squad currently.
Gerard Pique and Clement Lenglet will be partnered in the centre with rumours that Samuel Umtiti could be heading back to Lyon on loan. Jordi Alba will play on the left.
For the double pivot, Koeman has options but Frenkie De Jong is definitely a lock, with either Sergio Busquets or Miralem Pjanic featuring alongside him - expect those two to share minutes for much of the season.
And in attack there's Lionel Messi plus another three players. It's likely to be Antoine Griezmann playing through the middle as a false nine with Messi operating from the right, and Philippe Coutinho playing attacking midfield, as the No. 10.
The left is likely to be Ansu Fati but Ousmane Dembele will be pushing hard to beat him to the punch. There's also Trincao, who has been hugely impressive in friendlies and Koeman has shown admiration for him. But he'll probably need to make do from the bench for now.
Luis Suarez, Ivan Rakitic and Arthur have all vacated the club, being transferred to Atletico, Sevilla and Juventus respectively.