He already accepted this week that the league has been propelled into the realms of "vital" importance thanks to their FA Cup exit at the hands of Everton at the weekend. He more than anyone knows that Barry will in all probability ask to leave if Villa fail to finish in the top four.
However, it is the possibility of a herd mentality emerging this summer that will be most worrisome for the manager. It is especially unnerving that someone of Petrov's standing in the squad (he was given the captaincy in Barry's absence at Everton on Sunday) should accept publicly that his own contractual situation will be influenced by Barry's movements.
The Bulgaria midfielder, who has a strong bond with O'Neill having followed him from Celtic to Villa in 2006, is currently waiting for the club to begin negotiations for a new contract. Yet Petrov will be happy to wait until the end of the season, when a clearer picture emerges on whether Barry decides to stay at the club.
"Gareth staying would be a big influence on my future," he said, suggesting that he might not be the only one in the dressing-room maintaining an interest in Barry's future.
"If we keep Gareth it will also send out a message to all of the players, a big message that we are in for something big next year.
"We all hope he is going to stay because he is one of the best midfielders in the country and you try your best if you want to achieve something. We need to make it difficult for him to make a decision [to leave].
"There was a lot of speculation in the summer about Gareth leaving and we all wanted him to stay. He mentioned that if Villa could get in the Champions League, there's be no point moving and so far we've shown that we can be fighting for a top-four finish with the club where he has been for 11 years.
"If we can finish in the top three or four, we have a better chance of keeping a man who is probably the best player at the club."