McGregor damaged the ligament in his right knee during Saturday's defeat by Hibernian, little over 12 months after suffering the same injury in his left knee at Tannadice.
McGregor missed the vast majority of last season and faces another campaign in rehab.
But Lennon is sure the 27-year-old possesses all the mental strength to bounce back again.
"He has done his cruciate and it's a massive blow, we really feel for him," said Lennon, whose team face Motherwell in the Scottish Premier League on Sunday.
"But he has shown once before that he has got the correct temperament, character and drive to come through that. He came back very, very strong.
"He knows the hard and rocky road that lies ahead of him.
"I'll certainly be using Darren's situation to motivate the players on Sunday and should we get the victory we'll dedicate it to Darren because we're very much a family here and when one hurts, we all hurt."
McGregor was St Mirren's best player in his first season in Paisley after following Lennon from Cowdenbeath, but his progress has now been cruelly curtailed twice.
"It shows how fragile football is," Lennon said. "Someone with Darren's talent and drive is going to miss two years running but he is mentally tough and has a fantastic medical team round him and there is no doubt in my mind he will recover once again."