Kyrgios went to the net to shake hands with Nadal, who won 7-6 (7-0) 5-7 6-4 to make the semi-finals.
But immediately he slammed his racket on the ground. It sprung high, traveled half the length of the court and prompted a ball boy to take offensive action, moving out of the way to avoid being hit and potentially causing injury.
Gilbert wrote on Twitter: "It's ridiculous to see penalties be serious after such a good match."
Gilbert questioned whether this would happen, as the ATP, which runs the men's tour, only handed Alexander Zverev an eight-week suspended ban, as well as a fine, after the world number three took the umpire's chair. Violently hit his racket against him.
He said: "The stick could easily go anywhere like a stand and kill anyone, seriously terrifying seeing him in front of a large crowd.
Expressing regret for the incident, Kyrgios wrote: "I didn't want it to go anywhere near you to be honest."
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