Xevi Pujolar, the well-known F1 engineer who has switched from Williams to Toro Rosso, says Pastor Maldonado is "underestimated".
Pujolar has worked with what he describes as "great drivers like Mark Webber and Ralf Schumacher", but he says that was "not the same" as collaborating with Venezuelan Maldonado.
Despite his 2012 pole and win, Maldonado is often dismissed even by F1 insiders as a ’pay driver’ who gets caught up in too many accidents.
But Pujolar told Spain’s El Confidencial: "I have always said that Pastor and (Juan Pablo) Montoya are the drivers (I have worked with) who impressed me most.
"Maybe it’s because they are great fighters," he added. "Pastor has shown how fast he is but I think he is often underestimated."
Pujolar, who has also just left Williams, insisted the 2014 Lotus driver had "a good relationship with the team (Williams) when it was stable."