Jose Mourinho confirmed the club made a bid for the Manchester United striker on Wednesday, adding that the England international is his only transfer target ahead of the new campaign.
Cech has faced Rooney on 19 occasions during his Chelsea career and limited the striker to just nine goals, but knows the threat he poses and would enjoy seeing him lining up on the same team.
"Wayne Rooney is a great player but, at the moment, he's a Manchester United player," he told reporters.
"We'll see what's going to happen. He's a great player. Let's see.
"You always want to have the biggest and strongest squad so you can challenge for titles."
Chelsea's initial bid was rejected by the Red Devils, but Cech remains confident that Mourinho will establish a strong squad regardless of whether Rooney joins or not.
"That's why you have a manager and sporting director to take care of that, and all you (as a player) have to do is the work on the pitch," the Czech Republic international added.
"We already have a few more players in and a great squad. If the manager doesn't think we have enough he will try to get players in. It is only his decision.
"In football things are changing every day with every squad. As time goes on, every team can make some changes. Anything can happen."