Owner Mike Ashley put the club up for sale last month.
An offer worth up to £300million from Amanda Staveley’s PCP Capital Partners has been rejected by Ashley.
But a deal could still be agreed ahead of January’s transfer window, when Benitez hopes to strengthen his squad.
Barnes – who had a spell at Newcastle late in his playing career – doesn’t think Benitez will be looking too far ahead.
“The important thing is to be realistic about where you are and who you have,” said Barnes, who started his professional career at tomorrow’s opponents, Watford. “Newcastle have what they have.
“Rather than looking forward and saying if they can get more money they can get better players, I think Rafa will be focused (and thinking) ‘let’s worry about what we could do with more money and better players when we get more money and better players’.
“You have to be realistic and think ‘this is what we’ve got at the moment’. If it happens, it happens. But it may not happen.
“If it doesn’t happen, and people are getting excited, they will forget about winning these matches and playing these games.
“I’m sure that’s what Rafa’s focused on. Forget about the future and a takeover and there’s money to be spent.
“If there is, it would be nice. But if there isn’t, you still have to be competitive.”
Staveley was involved in the takeover of Manchester City by Sheikh Mansour in 2008. The club has since been transformed by money from Abu Dhabi.
Could United be transformed by a wealthy new owner?
“The fans are superb,” said Barnes, signed by Kenny Dalglish in the summer of 1997.
“It’s a huge stadium. The potential’s there, but what happens now, in the financial climate we’re in, is about money.
“Therefore, would you then say that Manchester City had the potential to do well? They did from a fans’ perspective. From a finance perspective, no they didn’t (until) somebody from Abu Dhabi buys Manchester City. Now they can do what they do.
“Once upon a time, we talked about potential being the size of the stadium and the fanbase. Whereas now the potential is about getting someone to put a lot of money into the club and spend. Then you can be a successful club.
“Newcastle are a huge club, as we know, and the fans are fantastic. It’s a huge stadium.
“I understand the passion that the fans have. It’s a fantastic city and I thoroughly enjoyed my time there, and for the fans more than anything I’d love to see them do well.”
Newly-promoted Newcastle are 11th in the Premier League.
“The first season in the Premier League is really about cementing your place there,” said Barnes. “As the years go on, you look to see if you can push into the top six. It would be hard for them to break into the top for, but cementing your place in the league’s the most important thing.
“Everything has been positive because of the fans’ support of Rafa. It means that they’ve done well.
“Under different circumstances, and under a different manager, it could have gone the other way. But the fact that the fans like him meant that they stayed with him and picked up.
“All you can ask any manager to do is maximise the potential of what he has at his disposal, and he’s certainly maximised the potential of that team.
“There are Premier League teams that have got better players than them, but they work well as a team, particularly as they’ve got a lot of foreign players and you’d say ‘are they up for a fight?’. Rafa’s galvanised them, and, with better players, he could do better.
“You can’t ask any manager to do better than how Rafa’s doing with the players he has.”
Barnes is an ambassador for Bonus Code. Go to bonuscodebets.co.uk.