Sterling joined Rangers from Chelsea last summer following a loan at Stoke City, but was largely on the fringes of the squad until last Thursday night.
He came on at half-time in Rangers’ 3-2 win over Real Betis in Seville on Thursday night and produced a solid performance in the middle of the park.
His showing in Europe earned him a place in the starting eleven against Aberdeen in the Scottish League Cup final and he was brilliant in the middle as Rangers won 1-0 at Hampden Park on Sunday.
Halliday conceded that he is not sure where Sterling has been all season given the way he seamlessly forked out two great performances.
He stressed that the player deserves more credit as played out of position in the middle of the park where it is not easy if someone is not a natural midfielder.
The former Rangers star said on Clyde 1’s Superscoreboard: “I am sure I am sitting here with other people and thinking, where has Dujon Sterling been all season?
“For me, his two performances since he came in have been nothing short of incredible.
“Players can play out of position, but I think the hardest position on the pitch to play out of position is central midfielder if you are not a midfielder.
“A lot less time on the ball, taking it in areas where you never really took it as a professional footballer and I thought his performances over the two games were exceptional.”
Sterling will be looking to keep his spot in the side as Rangers look to chase down Celtic in the title race.
