After providing an assist and a stunning free-kick during last weekend’s win at Leicester City, the No.10 scored again during the midweek 1-1 draw with Spartak Moscow in the Champions League.
McDermott is a big fan of the Brazilian playmaker and feels if he can get on the ball in the right areas of the field, Coutinho could cause Rafael Benitez’s side a lot of problems.
“Liverpool have got a lot of pace going forward but the Newcastle centre-backs are quick as well,” he told Liverpoolfc.com.
“If Coutinho plays and plays well you would fancy Liverpool to win because he is an exceptional player.
“He is a player that is capable of scoring 15 goals a season and if he can do that and the strikers contribute then we will win more games.
“I’m looking forward to it because Liverpool have got to start turning those draws into wins. They are playing superbly well but drawing a few games, and it’s the three points we are after.
“Some of the football Liverpool have been playing is fantastic and it has been a pleasure to watch it when I’m working at the club for the home games.
“I’m sure they would take the three points over a good performance on Sunday, but the Liverpool way is to play well and get the three points so it’s a difficult one to call, especially after Liverpool have been away in Moscow in midweek.
“If Liverpool play well I think they will win the game, but don’t rule out Newcastle because they will give them a real tough game.
“Rafa has got them well organised, he’s always done that wherever he has been, and all of the players know their jobs.
“Newcastle won three on the trot but then lost at Brighton last weekend so it will be a tough game for both sides.”
Asked to explain where his loyalties lie on Sunday, McDermott admitted his feelings will be split.
During his first spell in the black and white of Newcastle, the Kirkby-born midfielder played against the Reds in the 1974 FA Cup final.
After enjoying wonderful success at Anfield, he then returned to the north east to play alongside the likes of Kevin Keegan and Peter Beardsley at St James’ Park, before later becoming assistant manager to Keegan and then Kenny Dalglish.
And McDermott will therefore remain neutral come kick-off.
He said: “It depends which side you are looking at, either from Newcastle or Liverpool, and unfortunately I’m right in the middle!
“I remember a couple of months ago Kevin Keegan said if you cut him in half one part would be red and the other black and white, and that is the same for me.
“Whatever happens I won’t be jumping up and down in the stand due to respect for Liverpool and Newcastle so I’ll just sit there in case there is a camera on me!
“I just hope it’s a great game and the best team win.”