The 22-year-old midfielder is having a great season at Celtic, scoring five times in eleven appearances in all competitions.
His performances in Scotland earned him a call-up to the Denmark squad during the last international break and he made his debut for his country in their win over San Marino this week.
Hartson pointed out that the midfielder has added goals to his game and his ability to find a defining pass from midfield with his silky play makes him an asset for any team.
The former Celtic star is delighted that he finally got his hard work rewarded by getting his first Denmark cap against San Marino.
Hartson said on the Go Radio Football Show: “He is adding goals to his game.
“He has got that silky type of play to him, he is great to watch, keeps the ball very well and he has got that killer pass in him with the right weight.
“He is having a great season and I am absolutely delighted for him that he won his first Denmark cap.
“He’ll be absolutely thrilled with that and so will his family.
“It’s always great when you represent your country for the first time and hopefully it will be one of many more.”
O’Riley was the subject of interest from other clubs in the summer transfer window, but Celtic made sure to keep hold of him.
