Alastair Cook admitted his position as captain will become "untenable" if he cannot arrest his slump in batting form within the next three Tests.
Cook, who described defeat to India in the second Investec Test at Lord's as among his "darkest experiences", conceded he has suffered moments of doubt over his ability as captain and, for the first time, gave an indication of the time-frame he was giving himself to turn it around.
England, under Cook's captaincy, have lost seven of their last nine Tests and have not won any of their last 10. Cook has failed to score a century in more than a year - 27 Test innings - and is averaging just 14.33 in 2014.
"I said I'd do it until my position becomes untenable," Cook said. "If I'm not scoring runs by the end of the series and we're losing more games it becomes tougher and tougher. Clearly I'm not the man to turn it around.
"Everyone has doubts. When things aren't going well, of course you have your doubts. When I was made England captain I said to my wife that I was going to give it my all. If it's not meant to be it's not meant to be, but I want to be proud of the way I have gone about it.
"I believe the team needs me to lead them through this tough time. But if it gets to the stage where I am not scoring runs by the end of the series my position is untenable. To quit now in the middle of the series would be wrong. I'm not quitting at the moment.
"I've got an inner steel, which I've got to keep drawing on. First of all I've got to start scoring runs, a lot of things can change quickly from there. I hit the ball better here. I've got to back myself that a score will come. The recent past hasn't been kind to me but we have won games with me as captain and I've won a lot of one-day games as well."
For the first time, Cook also had some veiled criticism for his players. Accepting that his bowlers had squandered helpful conditions on the first day and his batsmen decent batting conditions on the second.
"We've got to have lads who are prepared to front up," he said. "I'm fronting up. I hope the lads in the dressing room will as well.
"A captain is only as good as the players who play. I've captained well at certain times. I've captained well at Trent Bridge. Here it was a simple game plan and I don't think my captaincy was the reason we lost this game.
"India out-batted and out-bowled us. It was a good toss to win but we didn't put the ball in the areas we would have liked to have done. Then, with the pitch at its best, we didn't take that opportunity with the bat, either. There are no excuses.
"A lot of the standout performances have been by the younger players, which is great the way they're handling Test cricket. The older guys aren't playing as well as their records suggest and that's hurting us. To win games of cricket we need at least nine or ten people playing really well. It's not happening for those guys at the moment, they've got to look at themselves. I've got to start scoring runs as well, that can only happen with a lot of hard work."
Peter Moores, England's coach, also offered Cook his supporting, describing him as "the right man" to lead England.
"He is not hiding," Moores said. "He knows he has been under pressure for a long time, in Australia and now. The first thing he is doing is starting to hit the ball better. He knows it is tough up here. Often under pressure he is at his best. He has said quite clearly he wants to carry on. He is up for the challenge. I think he is the right man for the job, I really do. It is a new team. We have to learn and improve quickly. We are getting match-winning moments and we are not taking them."
As well as the struggles of Cook and Prior, England's other senior players, Ian Bell, James Anderson and Stuart Broad, have failed to live up to their usual standards and Moores admitted it was something the selectors would have to look at.
"I knew it was going to be tough because the last time I came in we had lost some players. If you asked me if I thought it would be the senior players who were trying to find form and the younger players firing, I wouldn't have thought it would be that way round but it is what it is. This is a five-Test series."