The 25-year-old has been with his current side since 2021, featuring on 78 occasions in all competitions, scoring nine goals and registering 16 assists in the process.
Majer was a key player for Rennes during the 2022-23 campaign, making 42 appearances, contributing three goals and registering seven assists.
The Croatia international managed two goals and six assists in 32 Ligue 1 outings, while he scored once and provided one assist in eight Europa League appearances.
Majer only signed a contract extension with Rennes last October, with his current terms due to run until June 2027, but there has been speculation surrounding a possible exit this summer.
According to Italian journalist Fabrizio Romano, both Wolfsburg and Leverkusen have submitted offers for the attacker, with the Bundesliga pair in competition for his signature.
Romano claims that negotiations are at their 'early stages', but Rennes are said to be open to letting the Croatian leave this summer for the right price.
Majer started his professional career with Croatian outfit Lokomotiva, before representing Dinamo Zagreb for three years ahead of a move to Rennes in 2021.
The attacker has featured on 22 occasions for Croatia, scoring four goals in the process, while he made seven appearances at the 2022 World Cup.
Majer also played in both the semi-final and the final of the UEFA Nations League last month, appearing off the bench against Netherlands in the last four and Spain in the final.
Wolfsburg finished eighth in the Bundesliga during the 2022-23 campaign, one point behind seventh-placed Eintracht Frankfurt in the race for European football.
Leverkusen, meanwhile, were sixth, with the team qualifying for the group stage of the Europa League, which could hand them an advantage in terms of the negotiations.
Wolfsburg have already made three new signings this summer, bringing in Moritz Jenz, Vaclav Cerny and Cedric Zesiger, while Leverkusen have brought in Arthur and Alejandro Grimaldo, with the latter arriving on a free transfer from Benfica.