"Michael Duberry has been pretty consistent with what he said," said McInnes. "He had always said he would just do it until the end of the season.
"He has his family and four kids down the road."
Duberry, suspended for Saturday's visit by Aberdeen, arrived in Perth after having his contract with League One outfit Wycombe Wanderers terminated by mutual consent.
It would take a really fantastic offer to prize Jody Morris away from us
St Johnstone manager Derek McInnes
The defender who started his career with Chelsea before spells with Leeds United, Stoke City and Reading has helped steer St Johnstone clear of relegation trouble in their first season back in Scotland's top flight.
But, although McInnes believes Duberry has enjoyed his time at McDiarmid Park, he expects him to seek another club when his short-term contract ends.
"He's made a commitment to us and a sacrifice to us, which we have been grateful for, but I don't see that situation changing," said McInnes.
"I think if he could move St Johnstone down to North London, he would happily sign.
"He has made that commitment to us and it was always on the premise that it would be short-term.
"His family is important to him, like everybody, and I think he misses them.
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"The sacrifice he has made has been well received by everybody at St Johnstone, because he has done very well for us."
McInnes, meanwhile, expects another former Chelsea and Leeds player, Jody Morris, to remain with St Johnstone next season.
"Jody is contracted here," the Saints manager said of the midfielder who joined St Johnstone in 2008 after leaving Millwall.
"He has another two years left of his contract.
"It would take a really fantastic offer to prize him away from us. He is a key player for us."
Source: BBC Sport
Source: BBC Sport