He believes that over-training compromised the team's chances of winning the test series against the All Blacks...
Sean O'Brien's criticisms of the Lions coaching team have caused a stir and prompted an official response from the organisation.
He claimed that the Lions attempt to win the series against New Zealand was hampered by the players being over-trained.
This charge has been refuted by the British & Irish Lions Chief Executive, John Feehan.
Commenting on the statements he replied: "I said all along that I think we had the best coaching team available and I think they proved that in what we achieved in New Zealand."
"People will always have their views on what could have been done better but the fact is that, against all the odds and with limited preparation time, this squad became only the second Lions team in history to either win or draw a series in New Zealand in 13 attempts. That achievement cannot be underestimated."
Irish Times journalist Gavin Cumminsky joined Off The Ball tonight to discuss the controversy. He believes that Mr Feehan's statement is "highly disrespectful."
He added that Sean O'Brien should be "applauded" for offering his honest assessment of the tour.
The Leinster and Ireland player took to Twitter this evening to clarify that he offered his opinions with "the intention of building on what was a great tour."
"I have nothing but respect for Warren and the whole coaching team," he added.
Commenting on the training regime while the tour was on-going, Warren Gatland said:
"We freshened them up a bit and made the week a little lighter. When we looked back on the tape of the first Test, our forwards were a bit heavy-legged. We did a double session on the Thursday in the first Test week. I don’t think it was just the double session, it was the accumulation of three to four weeks of no days off, travel, the games, the trainings, walk-through, everything the coaches do, the meetings. So we consciously lightened up last week."