Former US Open champion Juan Martin del Potro said on Saturday that his return to tennis next week, following a two-and-a-half-year layoff, will be “more of a farewell than a homecoming.” Del Potro is expected to declare his retirement following his participation in the Argentina Open in Buenos Aires, his first tournament since fracturing his kneecap at Queen’s in London in June 2019. The former world number three has had four surgeries on his knee as a result of the accident, and is now ranked 757th in the world. Juan Martin del Potro, 33, who defeated Roger Federer in the 2009 US Open final,…