Sunderland manager David Moyes will need his summer signings to hit the ground running if he is to win the relegation battle he has forecast for his new side.
For the Black Cats have suffered the greatest losses from last season's squad among the 20 Premier League clubs, who on Wednesday concluded their transfer business until January.
Along with Watford, Sunderland have seen four of last season's most-used starting XI move on, while the departures from the Stadium of Light account for almost 42 per cent of last season's league starts and minutes played.
By contrast, perennial top-four challengers Arsenal, Manchester United, Chelsea and Tottenham - along with West Brom - have kept last season's most-used XIs together, while Leicester have lost only N'Golo Kante from their title-winning core.
Man United top the charts for stability, with 96.7 per cent of last season's starts and 95.4 per cent of minutes played belonging to players still at the club - though many of those may now find themselves as back-ups after the signings of Paul Pogba, Zlatan Ibrahimovic, Eric Bailly and Henrikh Mkhitaryan.
Moyes admitted last week that Sunderland's situation "can't dramatically change" from May's nail-biting escape, and the failure to complete a deadline-day deal for last season's loan star Yann M'Vila could be a setback to their hopes of progress.
M'Vila started 36 league games and played 3,189 minutes in 2015-16, and club-record signing Didier Ndong will have to quickly take up the slack, while £8million Papy Djilobodji, recruited from Chelsea, and loanee Jason Denayer must fill the central defensive void left by Younes Kaboul.
Goalkeeper Costel Pantilimon's departure during last season, coupled with Vito Mannone's injury, leaves Moyes relying on youngster Jordan Pickford between the posts, while full-back DeAndre Yedlin has also moved on, to Newcastle United.
Watford signed Kaboul but have lost Nathan Ake, Allan Nyom, Jose Manuel Jurado and Almen Abdi from last year's most-used XI. They and Sunderland - along with Swansea and Southampton, the two teams to have lost three first-team regulars - all go into the international break in the bottom seven of the Premier League table.