He, however, added that if the German refuse to re-sign the team then they might look at McLaren's Fernando Alonso as his replacement, Sport24 reported.
Commenting on Alonso's recent claim that he almost switched to Mercedes last year, Wolff said the McLaren driver had just explored his option, but could not negotiate with the Formula One Championship leaders.
Wolff revealed they failed to negotiate a deal with Alonso because they had promised to renew the deal of reigning world champion Lewis Hamilton.
Admitting that Fernando is 'one of the best drivers in history', Wolff said the McLaren driver has all the required qualities at the moment and Mercedes would definitely consider him if Rosberg refuses to renew his contract.
Rosberg is currently standing at the top of the championship table with a comfortable lead of 39 points over Ferrari's Kimi Raikkonen. However, his seven-race winning streak came to an end following a collision with team-mate Hamilton during the last weekend's Spanish Grand Prix.