Grigor Dimitrov has progressed at the Madrid Open after Donald Young was forced to retire during their first-round match.
World number 11 Dimitrov was leading 6-4 3-0 before a back problem made it impossible for Young to continue.
The Bulgarian will now face Italy's Fabio Fognini for a berth in round three.
Dimitrov reached the third round of last year's tournament before losing to Tomas Berdych.