Stefanos Tsitsipas has been punished after he received a warning for coaching during his second-round defeat at the US Open. The No. 26 seed squandered a match point as he suffered a 7-6(5) 1-6 4-6 6-3 7-5 loss at the hands of Daniel Altmaier on Thursday, and then confronted his opponent at the net for hitting an underarm serve.

That wasn't Tsitsipas' only problem during the match, as he also received a rare coaching warning. Coaching from the stands is now permitted, but a player's team can only give them instructions when they're both at the same end of the court. And he has now been fined for breaking the rules.

But Tsitsipas was playing on the other end of the Grandstand arena, across from his box, when his father and coach, Apostolos, started giving him verbal guidance.

At the time, the Greek star was 3-5 down in the fourth set, and Altmaier was serving to take the match to a decider.

The world No. 56 was bouncing the ball and preparing to serve when the chair umpire suddenly announced: "Code violation, coaching, warning Tsitsipas."

There were some murmurs from the crowd, but they continued playing, and Altmaier closed out the set, going on to win in four hours and 21 minutes.

Tsitsipas has now been fined for his coaching code violation and must pay £3.7k ($5k). It's a small fraction of his £114k ($154k) prize money, but it's unusual for a player to be fined for receiving coaching, given that most coaching from the sidelines is now legal.

There was another incident in the fourth set that Tsitsipas wasn't happy with, as Altmaier hit an underarm serve. The 27-year-old took issue with his opponent's tactics, and decided to air his grievances as they shook hands at the net.

"Next time, don't wonder why I hit you, ok?" he said. "I'm just saying, if you serve underarm... if you serve underarm."

Altmaier ignored the two-time Major finalist and said he didn't want to talk. The German will now turn his attention to his third-round clash with No. 8 seed De Minaur, while Tsitsipas has a fine to pay.

The Greek star recently rehired his dad as his head coach after their turbulent, on-off partnership came to an end last summer. Tsitsipas linked up with Goran Ivanisevic earlier this year, but they only worked together during two tournaments - Halle and Wimbledon - before splitting.

After linking back up with his father, Tsitsipas said: "It might not be something smooth that suddenly you see the right outcome out of it, of being back again with my father. That's not really what the whole point is.

"It is trying to figure out the person who cares the most about me and really is going to spend extra hours on the court, perfecting me, trying to get me as good as possible."

So far it hasn't been so smooth - Tsitsipas has not won back-to-back matches since the Barcelona Open in April. But he'll be hoping to regroup and come back stronger during the upcoming Asian swing.

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