Fernando Alonso says Ferrari must be convinced it is hiring a driver who is stronger than Felipe Massa if it decides to replace the Brazilian.
Massa's future at the Maranello team has been in doubt since the opening few races of the season. Several drivers, including Sergio Perez, have been linked to his seat in recent months.
Alonso labelled the drivers on that list as "little names" compared to Massa and his achievements in Formula 1.
"I've been working with Felipe for three years now and we have a very good relationship," said Alonso on Thursday in Singapore.
"If the team decides to change Felipe, anyone who arrives has to be better than Felipe.
"I've seen a lot of names written, and I don't know if they have been written with the head or the heart.
"With all the names you hear, if you compare what Felipe has done in Formula 1 and what these little names have done in Formula 1..."
The two-time champion stressed that another priority for Ferrari should be to find a driver who respects its tradition and is ready to work for the team.
"I think we need to respect the decision the team will make," said Alonso.
"In my opinion we need to have a driver that respects Ferrari, that respects the tradition that here we work for the team, for the red cars, and this is the first priority."
Massa, meanwhile, says he is just trying to keep his focus on doing the best job possible without worrying too much about his future.
"We need to carry on, trying to get good results, trying to do the best in the car, trying to put everything together," he said.
"That's what I'm always trying to do and that's the most important thing for me. My contract is not signed yet but I'm really looking forward to that."
- Felipe Massa
- Fernando Alonso