The outstanding Buddies midfield talent missed the Boxing Day draw at Inverness in order to undergo keyhole surgery and is already back on his feet.
Despite admitting his frustration at missing out on the final three games in Saints' unbeaten festive campaign, McLean is already plotting his comeback.
He said: "The surgery was minor and just a routine cartilage tidy up. It went well and I am now looking at being back within three to four weeks and hopefully that will mean I will be available for the semi-final with Celtic.
"It was a frustration to have to undergo surgery, but I was in some discomfort after the win against Motherwell and the scan showed that a tidy up was required and it was best to get it done quickly.
"With the winter break coming up it was pretty good timing although you never want to miss any game if you can avoid it."
The knee injury brings to an end a frustrating 2012 for McLean who had the second-half of last season decimated after breaking his collar bone back in January in a freak training accident.
A recurrence of that injury kept the Scotland Under-21 international out for another month, but he finished the season on a high last time around and has already reached a career-high six strikes this term.
That hot streak has already brought the talented midfielder to the attention of Nottingham Forest and Ipswich.
Meanwhile, MLS Dom Dwyer has confirmed that his trial with the Paisley club has come to an end.
The former Norwich City youth product, now with Sporting Kansas City, had hoped to join the Buddies on a short-term loan deal during in March. But it is understood that red tape on the other side of the pond has sunk his hopes.
He said: "Unfortunately, through no fault of the club, things have not worked out."