Del Potro overcame a scary late fall to beat Grega Zemlja of Slovenia 7-5, 7-6 (3), 6-0 Saturday, but said he twisted his ankle and hyper-extended his knee.
Del Potro hurt his left leg when chasing down a drop shot in the third set, skidding awkwardly on the grass and tumbling face first. He received treatment after taking a 4-0 lead and took a medical timeout after the next game, and returned to break Zemlja again to clinch the win.
The eighth-seeded Argentine said ''it was really painful. I was a little scared at that moment. ... Now I start to feel something in my knee and my ankle, as well. I will check with the doctor very soon.''
(For more sports news and updates, follow Ahram Online Sports on Twitter at @AO Sportsand on Facebook at AhramOnlineSports)