Zverev warned after taking photo of ball mark at Madrid Open

Top-seeded Alexander Zverev got a warning from the umpire for taking a photo of a ball mark during the clay-court Madrid Open after complaining about electronic line-calling.

The German player told umpire Mohamed Lahyani on Sunday (local time) there was a "malfunction" with the system after a backhand from local favourite Alejandro Davidovich Fokina was called in while Zverev thought it had gone wide during their third-round match.

Zverev then took a phone from his bag and took a photo of the mark, for which he received the warning for unsportsmanlike conduct.

After winning 2-6, 7-6 (3), 7-6 (0), Zverev posted the picture in an Instagram story with the caption, "Just gonna leave this one here. This was called in. Interesting call," flanked by two thinking emojis.