The Ibrox striker, 23, has scored 73 goals in 119 Rangers games but none against Celtic in 11 Old Firm derbies.

And the Colombian had a penalty saved by Fraser Forster as Rangers lost 1-0 to Celtic in Sunday's League Cup final.

"He's come to chances but the Celtic goalie was world class. Sometimes that happens," Ross told BBC Radio Scotland's Sportsound.

"At the end of the day, it's execution. It's a poor penalty. The boy has missed a penalty, big deal. We're talking about him missing chances, the goalkeeper's made some saves.

"He's in the right areas, he's performed well. He's messed Celtic about a bit."

Rangers captain James Tavernier, who had taken most of the club's penalties this season but did not convert three of them, handed the ball to Morelos in the run up to the spot-kick at Hampden. And manager Steven Gerrard said after the match Morelos had been the nominated penalty taker.

"We're complaining about a number nine hitting a penalty," said Ross, who won two league titles with Rangers as well as 13 Scotland caps. "Number nines should be hitting penalties. Full-backs shouldn't be hitting penalties. I was one, I know I certainly wouldn't be hitting the penalties."

Former Hearts and Hibernian midfielder Michael Stewart believes Sunday's match could prove to be a pivotal moment for Morelos, who was also denied by Forster three times in open play.

"It's a snowball effect, it magnifies," said Stewart, "I don't think prior to the game [on Sunday] there was a big psychological issue. It started to creep up. [The cup final] was a defining game and as the game wore on, you could clearly see it was playing on his mind.

"Morelos, in other games, he doesn't even think - it's bang and it's in the back of the net. He's got an unbelievable knack of just putting the ball in the back of the net.

"Fraser Forster has a great game but it takes two to tango. It's not all down to Fraser Forster that Morelos doesn't find the back of the net. I'll guarantee that Morelos going into 99% of his games wouldn't even think about who the goalkeeper was."