Costa won his second Premier League title under Antonio Conte in 2016/17, but their relationship turned sour the following campaign.
The striker claimed that Conte told him he wasn't part of his plans via text message, which eventually led to the 29-year-old returning to former club Atletico Madrid.
Clearly time hasn't healed much yet: Costa made his feelings towards the fiery Italian quite clear again on Wednesday night.
The Brazilian-born Spain international snapped a photo of the Chelsea lineup against Barcelona on Wednesday night for his Instagram Story, offering support to his former colleagues but drawing a line through Conte's name. The photo was shared to his 2.8m followers.
Chelsea lost 3-0 in their last-16 second leg. A double from Lionel Messi, taking the Argentine to 100 Champions League goals, sandwiched Ousmane Dembele's 20th-minute strike.
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