The manager admits he has followed 28-year-old McGregor’s progress for a number of years after his move from Cowdenbeath to the Buddies in July 2010.
The powerful stopper came up against Walter Smith’s title-winning Rangers side on two occasions in 2010/11 and on his first visit to Ibrox on April 16 that season he scored in a 2-1 defeat with Sasa Papac and Steven Whittaker on target for the Light Blues.
Two cruciate injuries then halted his career but after a frustrating two-year spell in which he featured in just 12 games he returned to Danny Lennon’s side in 2013/14 and was back to his best as he made 35 appearances in total and produced the type of form which has impressed the coaching staff at Murray Park.
McCoist, speaking exclusively to RangersTV, said: “Darren is a player Kenny, myself and Ian have always liked and appreciated. He’s a very wholehearted, committed, solid defender who is quick.
“He's had a little bit of a tough time and he was very unlucky with a couple of injuries he picked up at St Mirren.
“I remember him scoring here at Ibrox which we won’t hold against him but he’s a very, very quick defender and he’s obviously got over his injuries.
“He played in nearly 40 games for St Mirren last year and we just feel he’ll be a good acquisition for the squad.
“I went to watch St Mirren a good number of times last year and Darren was certainly one of St Mirren’s more experienced and more consistent performers.
“So it’s a tremendous opportunity for Darren to kick on again. He moved to St Mirren from Cowdenbeath and there’s always been progress with him.
“Someone like Darren will grasp the opportunity of coming to a place and an arena like Ibrox in front of 30 to 40,000 fans, it will only be good for him.
“We think the adrenaline rush and his desire to do well should be a perfect match.”
In May Chris Hegarty and Rangers came to an agreement which allowed him to move on and join Linfield while Emilson Cribari’s contract expired.
The signing of McGregor on an initial one-year deal will now give McCoist another option in defence as the League One champions attempt to get back to Scottish football's top flight at the first attempt.
McCoist added: “We definitely need options. We’ve lost a couple of defenders in the close season so I think it’s safe and fair to say that we are looking to strengthen in that area.
“Having said that I think our two centre backs last year scored something like 25 to 30 goals between them and along with the rest of the defence, and the rest of the lads, kept a very, very good number of clean sheets.
“But as I say we have weakened that defensive area in terms of numbers in the close season and we certainly need to strengthen it.”
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