Tonev last night completed a one-year loan move from Aston Villa, a club where the 24-year-old Bulgarian has endured a relatively inauspicious spell following his arrival in the Midlands last summer. He had been a target for then Celtic manager Neil Lennon, only for Paul Lambert to complete a £2.2m deal to sign the winger from Lech Poznan.
However, Tonev made just 20 league appearances last season and is now determined to kickstart his career at Celtic. Petrov, his compatriot and a confidante during a trying year at Villa, is certain that he will have no problem is settling into the Deila's plans.
"The biggest strength Tonev has is his pace," said Petrov, who left Celtic to join Villa in 2006. "Honestly, in footballing terms, he is lightning quick. He is also equally comfortable on either foot and switches from left to right without any difficulty. He can score goals and will provide plenty of assists. He is also strong.
"I believe the new Celtic manager has had Tonev on his radar for quite some time and he will be pleased to get him. He will fit into the new system very well.
"I'm positive Tonev will do well for Celtic. He is hungry to do well and desperate to play football and enjoy it once again. That is important. The last year at Aston Villa has been difficult for him but he has the mentality to put that behind him and concentrate on being successful at his new club.
"He called me from Glasgow to say he already he has a really good feeling about the club and that they have been very professional in their early dealings with him. The club has made sure he has been made to feel welcome and has everything he needs."
When Tonev joined Villa, Petrov - who still lives in the Midlands - took him under his wing to help the winger settle. Petrov then gave the Parkhead club a glowing reference about the player when they approached Villa to discuss a loan deal.
Similarly, Tonev, who has been capped 15 times for Bulgaria, asked his compatriot for advice on a move to Glasgow. "I told Tonev to join," said Petrov, simply. "He asked me about the history of the club and the supporters and I told him I had seven incredible years at Celtic and loved life in Glasgow, playing in front of the fantastic supporters. I wanted to leave to test myself in England and I also had a great time at Villa.
"He is well aware there huge demands at Celtic and that he will be expected to help the team win every game. He has the mentality to cope with that pressure. I'm sure the Celtic supporters will enjoy his style of play and they will take them to their hearts very quickly. I know he can help the club do well."