Carlos Sainz says he would be happy if his mentor and countryman Fernando Alonso tests the 2019 McLaren next year.
Zak Brown, the McLaren boss, has said Alonso is welcome to be a team tester and advisor even though he has retired from formula one.
"I would not mind if the driver who knows the cars best from recent years tests the car," Spaniard Sainz told Spanish publications this week.
"It would be positive for the team, and that's why it's being considered," he said.
2018 was a major low-point for McLaren, the once-great British team that had expected a strong recovery with Renault power after three disastrous years with Honda.
"Perhaps they thought they had more potential," Sainz said.
"They did not expect the car to be born as it was and that as the season progressed it would not respond well to updates.
"The work was then focused on analysing what was happening, not because the team didn't want to develop the car," he added.
For 2019, Sainz is also hoping for an improvement from Renault, so that both McLaren and the French manufacturer's works team "do not suffer so much on circuits with long straights".
Finally, he said he is hoping Liberty Media's plans start coming to fruition in 2019.
"The tyres are going to be similar, in fact for me very similar, but I think the new regulations will help us. We must give some confidence to Liberty, who have pushed for the change and will continue to push until 2021," said Sainz.