Roger Federer labelled the Italian Open ticket policy "strange" after some fans were left upset by rising prices.
Federer made the surprise announcement that he would compete in Rome for the first time since 2016 on social media, the day after his quarter-final exit to Dominic Theim at the Madrid Open.
The rise in the cost of tickets, though, has been criticised by some fans. They are unhappy with the Italian Tennis Federation's decision to double prices after Federer was announced.
"I heard about it and I heard some fans were not happy. That's disappointing to hear," Federer said.
"They [the Italian Tennis Federation] did it in a way that rewarded the fans that bought tickets earlier. Which is strange.
"It doesn't take away [from] the fact that I am happy to be here. I am personally very happy to be here and pumped up to play well."
The extra matches will keep Federer's match sharpness up heading into the French Open, where the 37-year-old is aiming to win his 21st Grand Slam singles title.
Poor weather in his native Switzerland, where Federer mostly practices, influenced his decision to head to Rome.
"The weather this week in Switzerland is not great," Federer added.
"I was playing well in Madrid so I said 'Let's come to Rome' - a city I like so much as well. There would be excitement. More excitement than me coming to a practice court in Switzerland."