Former Northern Ireland international Warren Feeney has warned that Bulgaria can be dangerous opponents with their fresh approach.
Bulgaria-based Feeney will be watching on closely when the two teams meet at Windsor Park in the World Cup qualifiers on Wednesday night.
The former Linfield, Newport and Ards boss is currently manager of Bulgarian second-tier leaders Pirin Blagoevgrad and has an inside track on Northern Ireland's next opponents.
Like Northern Ireland, Bulgaria finished bottom of their Nations League group in the autumn with two points, in a pool that also contained Wales and the Republic of Ireland.
They have since brought in new manager Yasen Petrov, who has a wealth of experience as coach in Bulgaria and China.
Petrov got off to the worst possible start with his side three down inside 13 minutes against Switzerland, but he made some attacking changes and Bulgaria were the better team in the second half before going down 3-1.
Bulgaria also lost 2-0 against Italy – the same as Northern Ireland did – ahead of Wednesday's Windsor Park clash but Feeney expects the new man to make an impact going forward.
"It's a difficult one because Bulgaria have brought in a new management team and it's funny, because one of my goalkeepers' father is the goalkeeping coach," Feeney told the PA news agency.
"There is a bit of banter between me and the staff because they're saying they are the better nation but I'm saying 'you are 29 places below us in the rankings'.
"But it's a difficult one because the new manager of Bulgaria is very experienced, he has managed abroad, and I think he will definitely change it. No disrespect to the previous one but they weren't scoring a lot of goals.
"It is difficult with players but I think he will bring a fresh mentality and it's a dangerous one for Northern Ireland because we haven't seen much of them yet."
Northern Ireland are also still adjusting to the end of Michael O'Neill's eight-year reign with former Under-21s boss Ian Baraclough looking for a second victory in 11 games on Wednesday.
Feeney believes patience is necessary during the transitional period.
"Michael did very well," the former Bournemouth striker said. "It took him a bit of time at the start but he got what he wanted. When you are qualifying, the expectation levels rise and people think we are just going to do it every tournament, but it's difficult.
"The good thing is Ian worked under him so he will know what way Michael worked but obviously Ian will be his own man again.
"The unfortunate thing with international football is that your older players aren't around forever and he has probably had a little bit of a transition now where there are younger ones coming through, which can only be good for Northern Ireland in the long run.
"He knows the players coming through and he had some very performances and results (with the Under-21s) which will have helped.
"We have got to have patience, people are getting appointed in the youth set-up and there will be a structure for him to move forward."
