The retirement of Roger Federer and Serena Williams last year has prompted many to debate who will be next to bow out, and Alexander Zverev thinks it will be Rafael Nadal.Zverev only recently returned to the tour after a horrifying ankle injury that he suffered at last year’s French Open in his semi-finals match against Nadal left him sidelined for six months.While the former world No. 2 is looking forward to being back on the court this year and striving to secure his first Grand Slam title, he believes it will also be the year that tennis will lose yet another legend.Talking to Eurosport about his prediction …