Johnny Manziel of Texas A&M has given his account of why he was forced to leave the Manning Passing Academy early, amid suggestions he had been drinking during his time as a counsellor.

The Heisman Trophy winning quarterback quit the Manning camp - an annual gathering of top-signal callers organised by Eli, Peyton and Archie Manning - in controversial circumstances earlier this week, but has moved to clarify the situation.

''I don't feel like I've done anything that's catastrophic,'' Manziel told reporters at the Southeastern Conference Media Day. ''Of course, I've made my mistakes. It's time to grow up."

He added: ''I was not asked to leave. It was a mutual decision.

'"The speculation of me being too hung over and that's the reason I missed the meetings is absolutely incorrect."

Manziel claims to have overslept after his phone had died, meaning he was unable to set a wake-up alarm, which prevented him from attending a meeting as part of his duties as a counsellor.

The 20-year-old was sharing a dorm with Alabama quarterback AJ McCarron, but was not woken by by his roommate.

Manziel, however, intends to return to the Manning camp next summer to work with the campers, while the QB also retains the support of Peyton Manning, despite the issues surrounding his departure this year.

"I enjoyed meeting Johnny," the Broncos quarterback told ESPN.  "I can remember a 20-year-old Eli [Manning] missing a meeting [at camp] and catching some flak.

"We always have counsellors who leave early. Johnny was great with the campers for the time he was here. He had to leave early. I wish him the best and I want him to come back as a counsellor next year."

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