Ronaldo is the all-time leading scorer in the competition, having netted 120 goals - 20 more than rival Lionel Messi.
It read: "I would like to apologize to all of Juventus fans for this misleading reaction in today's game".
"I am very happy to have scored my first double with the jersey of Juve and especially to have contributed to this important victory of the team", Ronaldo tweeted. I make it clear that this isolated attitude does not match what I have always shown in my career.
Cristiano Ronaldo is in line to make his first Champions League appearance for Juve after joining from Real Madrid, where he won the tournament in each of the last three seasons. He obviously hates YOUR football team and has no interest in synchronised swimming.
Costa later apologised for his late red card for elbowing and spitting at Di Francesco - the 24-year-old son of Roma coach Eusebio Di Francesco.More news: Philippines Typhoon: At Least 40 Trapped After Devastating Landslide
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On a Juventus corner, Gianmarco Ferrari attempted to head the ball down for his goalkeeper to collect but the ball came off the post and fell to Ronaldo who scored from a yard or two out.
"It's a very hard group, we know that we can do well and Juve must focus on being the best".
Stephan El Shaarawy and Bryan Cristante put them 2-0 ahead in under half an hour, but Chievo hit back after the break as Valter Birsa curled in a delightful effort and Mariusz Stepinski levelled with seven minutes left.
"It's human to be like that, sometimes we can't control our anxiety", he said.
Sky Sports Italia asked Allegri about the incident involving the Brazilian, and the manager said: "Maybe he was irritated at a foul before, but it doesn't matter, because this absolutely must not happen".
"Today, even though it was the first time with this system, we did well".