You must be qualified to play in the UEFA champions league europa league to play in europe so you have to be in the premier league if your an english team.
Arsenal was the 1997-98 champions.
Manchester United was the 1995-96 champions.
Manchester United was the 1996-97 champions.
Manchester United was the 1998-99 champions.
If Chelsea wins the Champions League, they will automatically be qualified for next year's no matter what their position is at the end of the season, and since the Premier League can only have four teams Newcastle would then not go to the Champions League but the Europa League, everything moving down one.