Brazilian still sidelined for visit of Crystal Palace due to lingering back injury.
Former long-serving Reds captain and current under-18s coach believes Jurgen Klopp lacks a holding midfielder.
Ojo impressed during England U20's World Cup winning campaign earlier in the summer.
Can has entered final 12 months of deal and remains in talks over an extension.
The playmaker was left out of the squad for Hoffenheim clash because of a back injury.
The Southampton defender continues to be linked with move away from St Mary's.
The 23-year-old is in the final year of his contract at Anfield.
Liverpool have thus far completed three summer signings - Solanke, Salah and Robertson.
Coutinho handed in a transfer request on Friday, 11 August.
The Brazilian playmaker handed in a transfer request on Friday following Barcelona bids.
Luan is dubbed as the 'new Ronaldinho' and as he has attracted interest from England.
Klopp believes he has a number of "hard decisions" to make ahead of clash with the Hornets.
Van Dijk has released a statement stating he wants to leave.
Messi's current release clause can be triggered for a fee of €300m (£272.2m, $353m).
Reds turned down a €100m offer for Coutinho from Barcelona this week.
Mohamed Salah is likely to make his Liverpool debut against Watford on Saturday.
Coutinho missed Liverpool's pre-season friendly against Athletic Bilbao due to a back problem.
Barcelona have identified Coutinho as an ideal replacement for Neymar.
Failed pursuits of Virgil van Dijk and Naby Keita have left Jurgen Klopp with work to do in the market.
Coutinho has been identified by Barcelona as Neymar's ideal replacement.
Former Reds midfielder Momo Sissoko urges Jurgen Klopp to consider bringing Mamadou Sakho into first-team.
Liverpool manager Jurgen Klopp was believed to be against the sale of Coutinho.