The former forward says he believes Barton still has a lot to offer and must prove he can play in the Premier League.
The midfielder left QPR at the end of last season with his contract coming to an end, and has so far failed to agree terms with a new club.
He had looked close to agreeing a deal with West Ham earlier this week, but after fans complained vociferously about any potential deal, the club decided to perform a U-turn and end negotiations.
And Hartson says Barton must now keep his head down and show he can still play at the top level because he will get a decent move somewhere.
“Joey obviously fancied a move to Upton Park but his reputation had gone before him. West Ham had a rethink and decided no,” he wrote on Kicca.
“He's worked hard on his personal side and in my view still has a lot to offer. He will get himself a decent move and then needs to keep the head down and show people that he can still play at the top level.”
Temperament issues have improved
The big issue for Barton now is that any more potential suitors will probably take a similar stance to the one West Ham.
While the talent has never been in question for the midfielder, he could certainly offer a lot to a number of sides, it is his off field antics and temperament that are likely to dissuade any interested parties.
Having said that, and as Hartson alludes to, that is a side of his game he has moved to improve in recent years, and some sides may think a move is worth the hassle if he would improve their squad enough.