India's Sumit Nagal advanced to the pre-quarterfinals of the Prague Challenger tennis tournament after his opponent Jay Clarke of Britain retired hurt here on Monday.

The 22-year-old Indian, playing his first competitive match since his Davis Cup encounter against Croatia's Marin Cilic in March, had received a bye in the opening round. Nagal, seeded sixth in the tournament that also features three-time Grand Slam winner Stanislas Wawrinka, will face local favourite Jiri Lehecka in the round of 16.