The Spanish side were powerless to prevent Partey heading to the Premier League after the Gunners triggered his release clause with LaLiga.
Speaking ahead of their first game without Partey this weekend, Simeone branded him an “extraordinary player".
“In these situations of the clauses we cannot give many opinions," said Simeone.
“They are decisions that are made based on that possibility that exists.
“As for Thomas, everything that happens to the guys who have given me a lot makes me happy.
“I remember the games we saw him with the B team and when he started to come through.
“He went to Almeria, it was difficult for him to find a stable place but he is an extraordinary player.
“He will do well and we wish him the best. We love him very much."