Australia captain Michael Clarke could walk away from international cricket after the Ashes series, according to former England skipper Michael Vaughan.

Clarke has struggled with the bat so far in this series and has scored just one Test century in his last 15 innings, which is his only score over 50 in that time.

Vaughan believes that he looks distracted at the crease and he could be focusing on retirement.

He wrote in The Telegraph: "As a captain when you go out to bat you have to be able to concentrate on the ball. Nothing else. You cannot go out to bat thinking about previous failures, what will happen in the future or battles you have had with selectors. I look at Michael Clarke and see a captain falling into that trap.

"I just wonder whether he is looking at the end. When you do that and sense you are in the final moments of your career, you start thinking about the finish rather than delivering in the here and now. I did that. I knew I had gone and was distracted by the future. I think it is evident from Clarke's batting he is not focusing on the ball and that comes from the mind being elsewhere.

"He is such a class player, averaging 50, so to struggle so badly in this series, and look so out of form, betrays what is going on in his head. I would not be surprised if he retired at the end of the series but for the last two games he has to try and find that energy and buzz to focus on the ball and play the way he can."

The fourth Test starts at Trent Bridge on Thursday.