His batsmen again fluffed their lines against spin as India romped to a six-wicket victory at Trent Bridge to take an unassailable 2-0 lead in the one-day Royal London Series.
Cook was at a loss to explain his team's frailty against Ravi Ashwin (three for 39) and his part-time helpers in the India spin attack as the hosts wasted an opening stand of 82 and ended up 227 all out.
India barely broke sweat, Ambati Rayudu making a career-best 64 not out, to pass the target in 43 overs.
After England's second trouncing in four days - they lost by 133 runs in Cardiff - Cook acknowledged they are not producing the cricket they should be.
"There are some good players there, who are not showing it. It's something we need to change around," he said. Discounting a one-off win against Scotland in Aberdeen, England have lost four of their last five ODI series.
The captain added: "Australia [last winter] was after a very tough Test series, and the Sri Lanka series was 2-2 going into the last one - and they played well in that match. But it is frustrating we are not playing to standards we know we are capable of."
The mitigation for England in Nottingham was a pitch that surprised everyone by offering conspicuous turn after Mahendra Singh Dhoni chose to bowl first.
Cook got out to Rayudu, the first batsman in inter- national cricket to do so. He said: "Ashwin and Ravindra Jadeja are very good at one-day cricket spin bowling. We had a few soft dismissals, and a few good balls as well. Every time you tried to build a partnership, you lost wickets, and that obviously keeps holding you back if you want to play aggressively."
That, he insisted, was England's problem, rather than that identified recently by critics, that they don't have enough power among their frontline batsmen.
"Everyone keeps talking about more power at the top," he said . "But we were 50-odd off 10 the other day, 50 off nine - we're getting good starts. The problem is that 40 was our top score at Cardiff, and 44 was our top score here … you're not winning games of cricket when you do that.
"We know how important big runs are at the top of the order - one of the top four or five going on to get a hundred or an 80 sets the game up … we're just not doing that at the moment."
Cook has gone 37 innings, back to June 2012, without an ODI century - and he knows that is far from acceptable, with the World Cup looming in Australia and New Zealand early next year.
He added: "Boundaries come when you start laying platforms, because naturally you're both more in, and can push the game on. But when you keep losing wickets - and there were some soft ones there - it keeps putting you back, and 227 wasn't enough."
India never looked back after Suresh Raina had Cook's opening partner Alex Hales caught behind sweeping, and Dhoni was full of praise for his team - including Mohit Sharma's direct-hit run-out of Ian Bell. "Bell's wicket was crucial, Raina's catch in the slips … those are the things that really help you as a team," he said.