Germany's world number two Alexander Zverev says he is facing a battle to be fit for the US Open following surgery on torn ankle ligaments at the French Open.Zverev only returned to the practice court last Sunday after the injury he suffered during his semi-final against Rafael Nadal at Roland Garros in June.He turned on his ankle during that match, screaming in pain when trailing Nadal 7-6 (10/8), 6-6 after three hours of play.He left court in a wheelchair, returning shortly after on crutches and in tears to announce his retirement, with Nadal going on to extend his record Grand Slam haul to 22, routing Norway's Casper Ruud in the final.Speaking in Hamburg at a press conference on Thursday the Tokyo Olympic champion Zverev said: "Obviously I am going to try to make it to the US Open even if it's in a very, very short time."Last week Zverev revealed that he suffers from type 1 diabetes, admitting he had struggled to accept his condition and had tried to hide it from the world.The last Grand Slam of the season starts in New York in a little over a fortnight on 29 August.If Flushing Meadows comes too soon Zverev is aiming to return for the 13-18 September Davis Cup group phase against France, Belgium and Australia in his native Hamburg.