The 21-year-old Northern Ireland international joined the club earlier today from Premier League side Newcastle and goes straight into the Blues squad for Saturday's npower Championship fixture against Hull City.
Ferguson's arrival at St. Andrew's comes less than 24 hours after West Ham loanee Rob Hall was forced to return to his parent club to have his groin injury assessed.
"Once the news came through about Rob Hall’s groin injury and going back to West Ham it was imperative that we could get someone in and thankfully we were able to do that," said Clark.
"We’ve hit lucky with Shane. He's a player I've tried to bring in since I came through the door. I must have asked the question on five or six occasions about his availability but Newcastle were never open to the idea as they had such a small squad and he was important to them. What has helped us are the acquisitions that Newcastle made in January.
"Newcastle think highly of him and gave him a five-year contract not too long ago. Everyone I speak to up there says he has done exceptionally well when he's played and I think he will be a big favourite with the supporters. A big thank you must go to Alan Pardew and everyone at Newcastle who made the deal happen for us."
Clark's association with Ferguson stretches back six years to when the Blues boss was a coach at The Magpies and Ferguson was a trainee just making his breakthrough with the reserves.
"He’s a lad who I have known for many years from my time on the coaching staff at Newcastle when he came into the club as a young schoolboy," he said. "I got to see him a few times in the youth team and I liked what I saw and I’ve just kept an eye on his progress.
"He’s predominantly a left-winger, but he can play anywhere on the left side. He’s quick, tenacious, has great desire and can cross a great ball. When he plays left-back he can put his foot in as well and he’s very competitive.
"He’s got a good pedigree for someone so young. He’s played in the Premier League and the Europa League and he’s an international footballer and he was desperate to come and play here."
Ferguson's arrival at St. Andrew's does not necessarily mean that Blues fans have seen the last of Rob Hall, but Clark admits it is highly unlikely he will return prior to the end of his loan spell officially ends on March 16.
"Rob did really well with seven assists," added Clark. "In hindsight in his last couple of appearances he was probably he hampered by the injury he has got now. His parent club West Ham want to assess that and see how it is but I would imagine even if it is a slight groin injury with him only having just over two weeks left of his current deal here it would be quite doubtful that he plays during that period.
“But we’ll certainly continue to monitor him because we felt he did really well and we liked what he did and brought to the group."