Kim Clijsters has announced her intention to come out of retirement and return to the WTA Tour in 2020. The Belgian first retired in 2007 to start a family but she returned to action in 2009 and won added two more US Open titles and the Australian Open title to her collection before announcing her second retirement in 2012. However, aged 36, she intends to come back to professional tennis on the WTA tour in 2020. Athletes coming out of retirement isn’t a new thing, though. There are many examples of sportsmen and women who, having decided to call it a day, were drawn back into competing. Some did it because they were bored, others because they missed the competition, others, well, because they missed the money! We’ve taken a look back at some of the greatest athletes who have unretired and made comebacks to professional sport. How will Clijsters compare to these stars when returns to the court?