"We have signed experienced players like Sylvain Armand, Foued Kadir, Emerson and Cheik M'Bengue," Montanier told staderennais.com. "Cheik, in my eyes, is one of the best in his position in France.
"Nelson Oliveira is a striker who has come from a big club in Benfica. Romero could surprise a few people. I know him a little bit, but Jean-Luc Buisine, who is in charge of our scouting department, has been following him.
"He is a striker for the future who is not far away from breaking into the national team. Our signings are good, at least on paper. Now they need to prove as much on the pitch."
Rennes currently sit fifth in the Ligue 1 table.