Much of the talk ahead of Friday night's World Cup qualifier in Stockholm has centred on Paris St Germain striker Zlatan Ibrahimovic and his potential to wreck Ireland's hopes of claiming the runners-up spot in Group C.
The 31-year-old has 33 goals already this season, and St Ledger said: "I have played against a few decent strikers in my time. He is up there. He's a very, very good striker. I think you could probably put him in a category with people like Messi and Ronaldo. He can win games by himself with magic moments."
Ibrahimovic's talent is well-known, but his critics argue he blows hot and cold.
St Ledger said: "Let's hope he has a cold one this week.
"To be honest, I have not seen too much of him. I wouldn't say I have watched loads and loads of games of his over the full 90 minutes, so it would be very harsh for me to judge him on that. You only see clips and nine times out of 10, he's brilliant."
Ireland boss Giovanni Trapattoni and his players flew out to Scandinavia this on Wednesday having completed the bulk of their preparations, and there is little doubt that Ibrahimovic would have come high on his list.
But St Ledger admits the Swede is far from the stereotypical big man up front.
He said: "When you play against big players, seven times out of 10 you would probably say they wouldn't be too good with their feet or they wouldn't be as mobile. But he seems to have the full package. He is obviously very physical, and he's got the feet. He seems quick enough over the ground, so he has got everything.
"Obviously, he's a very good player - you can't take that away from him. You give him the respect he deserves and then you just try to play your normal game."