Ferguson, a product of Rangers' youth system, previously spent 18 months in the Premier League with Blackburn following a £7.5m transfer in 2003.
However, he returned to Ibrox for £3m less after an injury-hit spell at Ewood Park during which he made 38 appearances.
"Barry has played at a very high level for Rangers, in big games," McLeish told the Rangers website.
"Maybe the Scottish league is not the strongest, certainly not anywhere near the Premier League, but he's played a good level of games, in the Champions League, the Celtic fixture and cup finals.
"I think he has got unfinished business in England. He started with a bad injury at Blackburn, then fought his way back to fitness, and the reports I got at that time, before he came back to Rangers, was that he was playing extremely well.
"But maybe he didn't stay long enough for people to make a full assessment of him. So I think in that respect Barry will want to come down with something to prove."
McLeish added: "They have barely started pre-season training but again, from the reports I've had, he's been up there in the fitness testing they have done. He's always been a pretty fit guy."
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