Alex Zverev takes a picture of the ball mark with his phone.
CNN  — 

Alex Zverev was given a warning for unsportsmanlike conduct after using his phone to take a photo of a disputed ball mark in the middle of his 2-6, 7-6(3), 7-6(0) win over Spain’s Alejandro Davidovich Fokina.

In the 10th game of the second set, Zverev was left bemused after a backhand from Davidovich Fokina was called in by the electronic line calling system.

After unsuccessfully protesting to umpire Mohamed Lahyani that the ball had actually landed out and there was a “malfunction in the system,” Zverev grabbed his phone and took a photo of the ball mark.

Zverev, the No. 1 seed in Madrid, later posted the photo on his Instagram Story with the caption: “Just going to leave this one here. This was called in. Interesting call.”

The ball mark in the photo posted by Zverev clearly appears to be three or four centimeters wide of the line with the electronic system seeming to deem a line swept into the clay as the edge of the court instead of the permanent white line.

While electronic line calling has been gradually implemented on grass and hard courts in recent years, clay-court tournaments have continued to use line judges and, for contested calls, umpires coming down to check the mark.

However, this season, the ATP has removed line judges from all events, while the WTA has also removed them from many of its tournaments. The one exception is next month’s French Open, which will continue using line judges for now.

It is just the latest incident involving the electronic line calling system this season after world No. 1 Aryna Sabalenka was also given a warning for taking a photo of a disputed ball mark at the Stuttgart Open just over a week ago.

And it wasn’t even the first such incident at this week’s Madrid Open, with former world No. 1 Victoria Azarenka also posting a photo of disputed mark on social media after her first-round loss to Olga Danilović.

Zverev, who is aiming to win the Madrid Open for a third time, will face Argentina’s No. 20 seed Francisco Cerúndolo in the round of 16 on Tuesday.