Had the two not been drawn to play each other in the last four and had eventually met in the final, a sixth placed finish in the Premiership would have been enough to qualify for next seasons UEFA Cup.
FA Cup Semi Final Draw:
Sunderland v Millwall or Tranmere
Arsenal v Manchester Utd
With Arsenal and Manchester Utd almost certain to qualify for the Champions League with a top four league finish, a team outside of the Premiership therefore are certain to gain European qualification next season by reaching the FA Cup Final - win or lose!
Here's the qualifying rules laid out at the Premier League official website:
The top two sides in the league qualify automatically for the UEFA Champions League. The teams that finish third and fourth qualify for the final qualifying round of the UEFA Champions League.
The fifth-placed team qualifies for the UEFA Cup, as do the FA Cup winners and the Carling Cup winners.
If a club already in Europe wins the FA Cup, the UEFA Cup place goes to the runners-up. If the runners-up are also already in Europe, the place will go to the next highest-placed league team.
If the winners of the Carling Cup are already in Europe the UEFA Cup place goes to the next highest-placed league team.