As Ferguson prepares to log- off from Ibrox this summer, however, his Old Firm rival is ready to commit his long-term future to Celtic Park.

At 22, Petrov - whose goal in Govan on Sunday virtually guarantees Celtic back-to-back SPL titles - is two years behind the Rangers captain in his development.

While the 24-year-old Scotland international believes he is ready to sample the rarefied atmosphere of the Premiership, the Bulgarian midfielder wants to continue his education under Martin O'Neill.

Petrov said last December that he had no intention of leaving Parkhead and would be keen to stay for at least four more years.

And after he embellished his reputation as one of Europe's most promising midfielders with another Ibrox derby goal, one of Bulgaria's greatest-ever play-ers advised him to stay in Scotland.

Having been hailed as 'the next star of Bulgaria' by legendary striker Hristo Stoichkov, the Parkhead youngster's progress is closely monitored in his homeland.

Now Emil Kostadinov - a World Cup semi-finalist at U.S.A 94 - reckons Petrov must stay in Glasgow if he wants to mature into a world-class talent.

Kostadinov, who played under Bobby Robson at Porto, insisted Petrov was correct to quit CSKA Sofia in a £2million transfer at just 19.

Even as a teenager, Petrov's talent was such that he could learn no more in the backwaters of Bulgaria's cash-strapped domestic league.

But, while Europe's elite must cherish the notion of luring the Bulgarian starlet away from Glasgow, Kostadinov believes O'Neill can help Petrov fulfil his immense promise.

'It will be better for Stilian if he stays at Celtic for at least one or two more years,' he said, having digested the impact of the 1-1 Old Firm draw on the SPL championship.

'It is only my opinion, but I know Stilian and he has done brilliantly in Scotland. He is still a young player, but he is also a very good player.

'We are fortunate to have many good young players coming through in Bulgaria. But Stilian is the best and has already captained the national team.

'He will be very important for the national team as we look towards Euro 2004. Everyone in Bulgaria watches Stilian and how he does.'

Kostadinov, who also left his homeland at an early age to pursue fame and fortune with the likes of Bayern Munich and Fenerbahce, does not believe that exposure to the glamourous continental leagues would hasten Petrov's rate of development.

Petrov has already indicated he can thrive in exalted company, having scored a Champions League goal against Juventus in the Stadio delle Alpi.

He again seems destined to sample Europe's premier club competition next season, with Celtic requiring just three wins from seven games to retain the title.

But he is in no hurry to follow the trail of talented midfielders out of the SPL, one that already has led Giovanni van Bronckhorst and Claudio Reyna to the Premiership.

'I think Stilian is doing well at the moment in Scotland, ' added Kostadinov, who now works as an agent having retired from playing at the age of 34.

'It was better for him to leave Bulgaria when he did. All the best young players in Bulgaria leave the domestic league before they are 20.

'If they get away from Bulgaria at an early age, it can make them better players. But I don't know if it would make Stilian any better to leave Scotland now.'

Petrov might ask advice from club captain Paul Lambert on the task of defeating Belgium and Croatia, with Bulgaria having been paired with Scotland's erstwhile World Cup rivals in a qualifying group for Euro 2004.

And with Lambert having accepted the advice of O'Neill to prolong his stay at Parkhead, the Celtic boss will desire that Petrov heeds the words of Kostadinov and lingers in Paradise.

'A few months ago, they asked me about a new contract,' Petrov said recently. 'I want to extend my contract and I would be really happy to stay.

'I want to concentrate on Celtic because I think I am improving as a player here. Everyone has a different vision of the game, some prefer to play in England or Spain.

'But I have learned things on the pitch here and off the pitch, as well. If I stay for another four years, it would be absolutely great for me.'

Given his penchant for scoring goals in the heat of Old Firm conflict, it would also be great for Celtic were Petrov to fulfil his wish and stay longer in the SPL than Ferguson.

'Stilian is not the next Hristo Stoichkov, but he will be the next star of Bulgaria,' said Stoichkov, when Petrov arrived in Glasgow three years ago. 'He has an incredible talent and will become a superstar.'