An offer of €12m was submitted for Guirassy, 24, but Reims turned it down.
Rennes have turned their attention to Morelos, the second highest top scorer in the 2019-20 SPL season.
Morelos joined Rangers from HJK Helsinki for €1.2m in 2017 and has gone on to score 77 goals in 137 matches.
Despite some disciplinary issues, Morelos is a well-rounded striker and Rangers boss Steven Gerrard has blocked an exit several times.
But the Scottish side have agreed to let Morelos go this summer if anyone meets their €15m valuation.
Foot Mercato reports that Rennes are ready to make an offer approaching €15m for 24-year-old Morelos.
However, Premier League sides are also keen on the Colombian international and could provide competition for Rennes.