The former England captain was appointed until the end of the season in April but failed to pick up a point.
Granada will finish bottom of La Liga and Adams said: "This season has been a disaster, we must not make the same mistakes.
"The main error has been signings. The owner is aware that he has made many mistakes, but this is a long project."
Adams' immediate future is unclear.
He has insisted that he will not stay on as coach but has been working at the Spanish club as a consultant since November and is vice-president of the company owned by Granada's club president.
Granada scored three goals in his seven-match reign.
At the top of the table, Real Madrid are three points ahead of nearest rivals Barcelona. Real travel to 11th-placed Malaga while Barca are at home to ninth-placed Eibar in Sunday's final games of the season.
Match ends, Granada CF 1, Espanyol 2.
Second Half ends, Granada CF 1, Espanyol 2.
Attempt missed. Martin Hongla (Granada CF) right footed shot from outside the box is high and wide to the right following a corner.
Attempt blocked. Jeremie Boga (Granada CF) right footed shot from outside the box is blocked.
Corner,  Granada CF. Conceded by Víctor Álvarez.
Víctor Álvarez (Espanyol) is shown the yellow card for a bad foul.
Foul by Víctor Álvarez (Espanyol).
Martin Hongla (Granada CF) wins a free kick on the right wing.
Víctor Álvarez (Espanyol) wins a free kick in the defensive half.
Foul by Isaac Cuenca (Granada CF).
Attempt blocked. Sverrir Ingi Ingason (Granada CF) right footed shot from outside the box is blocked. Assisted by Héctor.
Substitution, Espanyol. Hernán Pérez replaces Leo Baptistao.
Substitution, Granada CF. Jeremie Boga replaces Entrena.
Substitution, Espanyol. Víctor Álvarez replaces Pablo Piatti.
Attempt missed. Martin Hongla (Granada CF) right footed shot from outside the box misses to the left. Assisted by Adrián Ramos.
Attempt saved. Isaac Cuenca (Granada CF) right footed shot from the right side of the six yard box is saved in the centre of the goal. Assisted by Adrián Ramos.
Offside, Granada CF. Héctor tries a through ball, but Adrián Ramos is caught offside.
Attempt missed. Jean Carlos (Granada CF) right footed shot from outside the box is just a bit too high.
Substitution, Granada CF. Martin Hongla replaces Uche.
Jurado (Espanyol) wins a free kick in the defensive half.
Foul by Uche (Granada CF).
Attempt missed. Leo Baptistao (Espanyol) right footed shot from outside the box misses to the left. Assisted by Gerard Moreno.
Dangerous play by Víctor Sánchez (Espanyol).
Sverrir Ingi Ingason (Granada CF) wins a free kick on the left wing.
Corner,  Espanyol. Conceded by Héctor.
Pablo Piatti (Espanyol) is shown the yellow card for a bad foul.
Foul by Pablo Piatti (Espanyol).
Rene Krhin (Granada CF) wins a free kick in the defensive half.
Attempt missed. David Lombán (Granada CF) right footed shot from outside the box is close, but misses to the left from a direct free kick.
Marc Roca (Espanyol) is shown the yellow card for a bad foul.
Foul by Marc Roca (Espanyol).
Entrena (Granada CF) wins a free kick in the attacking half.
Jurado (Espanyol) wins a free kick in the defensive half.
Foul by Uche (Granada CF).
Substitution, Granada CF. Jean Carlos replaces Andreas Pereira.
Attempt missed. Andreas Pereira (Granada CF) right footed shot from outside the box misses to the left. Assisted by David Lombán.
Leo Baptistao (Espanyol) wins a free kick in the defensive half.
Foul by Sverrir Ingi Ingason (Granada CF).
Attempt missed. Uche (Granada CF) right footed shot from outside the box misses to the left. Assisted by Isaac Cuenca.
Gerard Moreno (Espanyol) wins a free kick in the attacking half.
Tony Adams called Granada's season "a disaster" after he lost his seventh and final game in charge against Espanyol.