By TALES AZZONI and HOWARD FENDRICH MADRID — Rafael Nadal is retiring from professional tennis at age 38, he announced Thursday, after winning 22 Grand Slam titles — 14 at the French Open — during an unprecedented era he shared with rivals Roger Federer and Novak Djokovic. Nadal has competed infrequently the past two seasons because of injuries and said next month’s Davis Cup finals will mark his farewell to the sport.