Last updated on .From the section Celtic

Stiliyan Petrov (right) was in Scotland to support a charity event organised by former Celtic team-mate John Hartson

Stiliyan Petrov says the lack of a challenge to former club Celtic is "not healthy for Scottish football".

Celtic are one win away from a seventh successive Scottish top-flight title and could win back-to-back domestic trebles.

Petrov, 38, won four league titles, three Scottish Cups and three League Cups during his seven years in Glasgow.

"One big club in a competition is not interesting," said Petrov, who first joined Celtic in 1999.

"You need another few clubs to compete and make sure the league will improve, but at the moment it's just a one-horse race.

"I think it's still a big gap and a long way to go for Rangers.

"As a Celtic fan, I am delighted because more success for Celtic is better, but it's not healthy for Scottish football and Celtic as well, because they need someone to compete with."

Rangers, beaten 4-0 by Celtic in Sunday's Scottish Cup semi-final, trail their Old Firm rivals by 12 points in the Premiership and are only ahead of Aberdeen on goal difference - and with Hibernian three points further behind.

The Ibrox side finished third last season, having won promotion to the top flight.

"At the moment, if you look at it, people don't take Rangers as a threat, it's more Aberdeen or Hibs," said Petrov at the John Hartson Foundation Annual Golf Day. "Rangers are not one of the biggest clubs.

"People always say Celtic v Rangers will always be one of the big rivalries, but if Rangers don't challenge, it will lose its intensity and it's important for Scotland.

"That's what Scottish football is all about; the Old Firm and that's why people all around the world love Scottish football.

"If that doesn't come back, it will be very difficult for Scottish football to recover.

"At the moment, Celtic can drop 10-15 points without a problem and still be champions. Before, we knew that, if you drew or lost a game, that was the end of it and that was what kept us on our toes or in the European games, because we had to be on top form every single week.

"At the moment, I don't think Celtic have been pushed or been challenged."