Hi Emarbe: The sentence is similar to what is commonly heard, as Nick indicates; but there is a simpler way to communicate this idea, as follows: "I saw u2 concert". "I attended a u2 concert." "I was at a u2 concert."

Yes, but the trouble is that the sentence is ambiguous. It's not wrong, but it could mean either 'I saw a concert performed by U2' or 'I saw a concert while sitting by U2.' Everyone will know what you mean, and native speakers do this all the time, but it's best avoided.