The French side, who are preparing for Champions League football after finishing third in Ligue 1 last season, have been looking at a deal to sign Slimani from Leicester.
However, they are now set to end discussions due to having reached an agreement with Amiens for Sehrou Guirassy, according to French radio station RMC.
Rennes have agreed a fee of around €14m to sign the striker, who is expected to put pen to paper to a four-year contract at the club.
Guirassy will undergo a medical at Rennes on Thursday morning and the club will have the striker they have been targeting.
Slimani, 32, spent last season on loan in Ligue 1 at Monaco.
The principality outfit though opted against triggering an option to sign him on a permanent basis, despite him hitting nine goals in just 18 league games.
Leicester splashed out £28m to sign Slimani from Sporting Lisbon in the summer of 2016.
