Bardsley, who was breaking into the first team alongside Ronaldo, noted that only former boss Sir Alex Ferguson truly foresaw the heights Ronaldo would reach.
Now retired after over 300 Premier League appearances, Bardsley described having a front-row seat to the making of a football legend.
“He'd come in with his quirky little jumper on, with these little braids coming down, and everyone was like, ‘Who's this kid?’" Bardsley told talkSPORT.com.
“The first-team players were aware because he played against them in a pre-season game (for Sporting) and he was magnificent in that game. I think that's what attracted interest from the club to go and pursue him and sign him.
“But when he came to the club, he was very slight, not much English at the time, but you could see glimpses of something.
“It wasn't until the following season when he had a bit more of an understanding and seeing first-hand how good he was. But it took time.
"Even from the day he walked through the door, you can see the professionalism and where he wanted to be in his career.
“He's obviously a gym addict. But everything you want to be an elite footballer, he had it. And that's a credit to him.
"You can see the longevity in his career and that's probably down to those things, the professionalism, the desired discipline that you need to stay at the top.
“He was one of them who spent money on himself, but obviously to help his career progress. I think he was one of the first to employ a chef.
"So all this sort of stuff, home gyms, chef at home, ice baths. He was doing this 20 years ago when people were not even thinking about it."