So when he walked out with Joe Root after Australia had been efficiently dispatched in the morning session, he appeared determined to put such negativity behind him - what followed was a skittish cameo.
Like a golfer who had remodelled his swing overnight, he came out with a new modus operandi. His aggression sent a message back to the dressing room: there can be no hanging around if this test is to be won.
The trouble was, his form has dipped sufficiently to undermine such a radical departure from his standard approach. He was trying to accelerate but velocity is limited when the ball refuses to find the middle of the bat. Try as he might, no one could accuse him of bullying the opposition.
His fidgety impatience appeared to be catching. After Root was dismissed by a beautiful Ryan Harris seamer, Jonathan Trott joined Cook in a nervy quickstep. Where once his entire working method was to bore an opponent into submission, Trott too set out as if involved in a T20 finals day.
As the pair played so palpably against type, flashing and nicking, it was like watching a couple of operatic tenors trying to rap. You knew it could not last. The captain was the first to go, thrashing inelegantly at a wide ball from the admirable Harris and snicking a catch to Brad Haddin.
Cook started in the job as if determined to buck the trend evident in the experience of Michael Vaughan and Andrew Strauss which insisted that the England captaincy inevitably erodes an incumbent's batting. He was imperious in those early days, as close to a banker as it is possible to be in a game as fickle as this. But this series, the weight of the job appears to be taking its traditional toll.
The relentless public duties of the Ashes have dimmed the brightness in his eyes. When the microphone is thrust under his nose, you can almost see his shoulders sagging. Cook is a captain who leads from the front. He is not gung-ho, not big on Henry V oratory, chirpy back-slapping and on-field chivvying. His leadership is described by personal performance. It might be politic to say it is the team that matters, but he knows his effectiveness as captain is diminished if he is not batting well.
How thankful he must be that he has centurymaker Ian Bell - unlikely ever to be emasculated by captaincy - in his team.