#2 Dembele-Messi-Griezmann-Suarez
If Coutinho does leave Barcelona or if he is out of form, Ousmane Dembele will be the man to replace the Brazilian in this forward line. Dembele offers a brutal pace and flexibility to the line-up. In fact, we could see the rise of Dembele as a Barcelona player in this formation.
However, Malcom could also be a part of this formation depending on the competition and the availability of the players.
#3 Coutinho-Griezmann-Messi
Suarez has had the worst season of his Barcelona career the previous campaign and if the 32-year-old cannot get back to form, we could well see him dropped from the starting XI. If Valverde needs to have a balanced approach, he can employ a 4-3-3 formation and his front three could be Coutinho, Messi, and Griezmann.
While Coutinho will occupy the left-hand side, Messi can do the honors on the right flank. Griezmann will be the central forward in this case. Based on how the game goes, Valverde will have a solid bench strength to make an impact as substitutes.