Former Republic of Ireland manager Mick McCarthy has earmarked Steven Fletcher as Scotland's biggest threat ahead of the Euro 2016 qualifying clash between the two sides.

Scotland host Ireland at Celtic Park on Friday night, with both sides looking to continue their encouraging start to their respective Group D campaigns.

However, McCarthy, who was Fletcher's boss at Wolverhampton Wanderers when the striker was in the international wilderness, has warned his former side that the Sunderland man is of the highest quality.

"I was his manager when he wasn't playing for Scotland. I could never understand that to be honest. Well I can and I can't but it was just a shame because he was playing well then," the Ipswich manager told reporters.

"When I was asked about Fletch by other managers I said he could play in the top four teams in England. If it was a Champions League team looking for a centre-forward, I would have hung my hat on him. Without any doubt. I think he's that good. He's still a young man, he's only 27 and should be at his peak. Unfortunately some of the injuries have restricted him from playing.

"Honestly, I thought he could have played for any one of the top four teams. I don't see him much now but I saw his goals against Crystal Palace and I thought his header was fantastic and his second was the finish of a real, cold, calculated predator. And he used to work at it, day in, day out, with Terry Connor, my assistant. And he loved it, he works hard at his game."

Ireland currently sit second in Group D on goal difference, three points above Scotland.