Adrian Grenier — REGRETS Suggesting Bieber for ‘Entourage’ Movie

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Adrian Grenier tells our sources … he wishes he NEVER named Justin Bieber as the ideal cameo for his upcoming “Entourage” movie … but still insists the dude could be a great actor under the right conditions.

Grenier — sporting a cool new samurai-style hairdo — was leaving The Sayers Club in L.A. last night when we asked about recent comments he made to about Bieber … when he said, “I saw [Justin”s] documentary and thought he was so cool. I think he would be great!”

But last night, Adrian pulled a 180 … telling us, “Why did I even say it I started something I didn”t want to finish … so, I don”t want to talk about it.”

Still, Adrian says Justin has the potential to be great on screen … because under the right circumstance … “Everybody can act.”

Adrian says he also feels Justin”s pain when it comes to criticism about his personal life … and can relate to JB”s urge to race Ferraris.

Check out the clip.