The Sky Sports pundit feels Champions League football would be the difference between having to sell the Frenchman and keeping him at St Mary's.
The 25-year-old is arguably Ronald Koeman's most influential player in the top flight, with his presence in midfield proving vital so far this season - his recent injury serves as a huge blow for Koeman.
And the Sky Sports pundit feels Schneiderlin could be persuaded to stay with the Saints if they secured Champions League football.
"Champions League football would enable them to go to the next level and become a place where players could fulfil their ambitions, rather than seeing Southampton as a stepping stone," Redknapp said.
"It's the difference between having to sell Morgan Schneiderlin in the summer because he wants to be playing against the best in Europe, to saying to him, 'why would you want to go to Tottenham or Arsenal when we've beaten them to a Champions League place?'"
Schneiderlin has long been linked with a Southampton exit, the Daily Mirror having speculated about interest from Manchester United, Arsenal and Tottenham this month.
Redknapp's point, however, stands. The Saints won their first game at Old Trafford for 27 years last weekend and sit third in the Premier League table.
Who's to say Schneiderlin is destined for a Southampton exit even if Koeman's side don't make the top four, meanwhile? The South Coast club managed to keep the Frenchman at St Mary's this summer and it proved inspired business. Saints fans will no doubt hope for more of the same this calendar year.