Boyata attracted interest from Fulham earlier this summer, while he could seal a move to Sevilla before the La Liga transfer window closes at the end of the month.
Petrov, who won four Scottish Premier League titles with Celtic, has now offered his verdict on the situation involving the 27-year-old.
"It’s really sad to see, you know,” Petrov told BT Sport.
"When you’re a footballer you like to play for a club like Celtic, you like to perform at the highest level.
"It doesn’t matter where you are, if you do it here, you can do it somewhere else, it goes without saying."
Celtic transfer news: Stiliyan Petrov gives Dedryck Boyata verdict after AEK Athens defeat (Image: GETTY)
Petrov’s former Celtic team-mate Chris Sutton pulled no punches as he reacted to the AEK Athens defeat.
And he singled out Boyata, who has 12 months to run on his contract in Glasgow.
"The blame game has to stop and it’s time for cool heads at Celtic," Sutton wrote on Twitter.
"The manager and board could have handled things better!
"Celtic’s poor recruitment is the reason they are out!
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Celtic transfer news: Stiliyan Petrov gives Dedryck Boyata verdict after AEK Athens defeat (Image: GETTY)
Celtic transfer news: Stiliyan Petrov gives Dedryck Boyata verdict after AEK Athens defeat (Image: GETTY)
"I don’t care about disco lights.
"Time to sort this mess out starting with Boyata."
Celtic will be looking to bounce back from the loss to AEK Athens when they return to domestic action this weekend.
Brendan Rodgers’ men visit Firhill to take on Partick Thistle in the second round of the Scottish League Cup on Saturday.