The fullback has spent this season on-loan at Betis, helping them win the Copa del Rey.
There has been calls for Betis to sign him permanently, but Haro said: "He is an excellent player, but he is owned by Arsenal and he must return there.
"He has felt the spirit of Betis Sevilla and we will see what can happen."
Haro also confirmed Joaquin will play on next season.
He continued: "Joaquin has decided to stay, he said it during the celebrations for the Copa del Rey.
"We already have a verbal agreement with him to stay."
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