This season has seen a rash of players failing to turn out for their sides, either because they are refusing to do so or because managers feel they are having their heads turned by other clubs.
Stoke goalkeeper Asmir Begovic was the latest example in Tuesday night's Carling Cup match against Shrewsbury, much to the annoyance of boss Tony Pulis, who branded the player's actions "disrespectful".
"You can understand Tony's anger because he wants to be able to pick all the players that are available to him," Barnes told Sky Sports News.
"I think it's important for a player to realise he has a commitment to the club that's paying his wages.
"Until such time as a deal is made for you to play for somebody else, any player has the obligation to keep giving his best with the club he's currently at.
"It wouldn't be in the player's interest or the club's interest to say, 'I'm not going to play'. The club could fine him. We don't want to reach that situation.
"We'd hope to reach a situation where both parties are happy moving forward."
Barnes cited the example of James Milner, who continued to play for Aston Villa in the run-up to his move to Manchester City, as being more typical.
"The vast majority of players would do that," he said.
"I don't know the details of the Begovic case but it obviously isn't ideal when a player refuses to fulfil the terms of his contract.
"I can't help but think somewhere in the background there's perhaps an agent whispering in the player's ear saying, 'we don't want you to be cup-tied to prevent a potential move'."
Source: Team Talk
Source: Team Talk