Watching Petr Cech play for Arsenal is "killing" Jose Mourinho, according to former Chelsea assistant manager Steve Clarke.
Cech, despite the misgivings of Mourinho, completed a £11million move from Stamford Bridge to the Emirates earlier this summer, with the deal sanctioned by Chelsea owner Roman Abramovich.
The Czech Republic international goalkeeper made his unofficial debut for Arsenal in the Barclays Asia Tour 2015 final against Everton, and Clarke believes watching the former Chelsea player come out in a rival team's colours would not be something Mourinho would have enjoyed too much.
"For me, he's still one of the best goalkeepers in the world," Clarke told Talksport. "He's a great signing for Arsenal.
"I smile a bit when I see Jose's [public] comments [over the sale of Cech, which has been tempered] because I know inside it will be killing him having to sell one of his best players to a title rival."
Nemanja Matic also had the same feelings over selling Cech to Arsenal, with the midfielder admitting he wasn't too happy seeing Cech sign for another big club in the Premier League.
"Petr is a great guy and a great keeper," Matic said. "It is going to be a very important signing for them.
"But I am not happy. We know that he is very professional. He is one of the best keepers. And I hope this season he does not perform as he did here for 10-11 years.
"I am happy for him because he gets to stay in London, which for him and his family was very important. I wish him all the best."
Branislav Ivanovic, another Chelsea stalwart, and one who played with Cech for a number of years, was also asked about the goalkeeper's transfer to Arsenal, and the defender gave a diplomatic answer.
"This is football, he wanted to play," he said. "I can say only 500 times thank you to him -- he gave us so much pleasure to enjoy the history of the club, winning trophies.
"As a person we will miss him in the changing room. His decision was he wanted to play and I wish him all the best personally.
"Just try not to win any trophies!"