Novak Djokovic received some parting advice from former coach Boris Becker after they announced on Tuesday they were to cease working together.
"He has not spent as much time on the practice court as he should have in the last six months and he knows that," Becker told Sky Sports News.
Becker said that the Serb would have to return to a more rigorous training regimen if he is to regain the number one spot he lost to Andy Murray this year.
"Success doesn't come by pushing a button. You have to work your butt off, because that is what your opponents are doing."
Djokovic won the French Open in June, but has gone through some poor form since then.
However, Becker said the two were in agreement over the end to their partnership and he would keep cheering for Djokovic.
"Such a decision does not happen overnight, it was a process," he said of the split, adding that it was "consensual."
"I am also convinced that he will become the most dominant player again, but he has to get back on the practice court and put in the necessary hours."
"Novak must concentrate on what has made him strong."