Brazilian driver Felipe Massa has described Ferrari teammate Fernando Alonso as the toughest opponent in his 10-year Formula One career.
"I've always had strong teammates but in the past few years the challenge has been even greater," Massa said Thursday, reports Xinhua.
"He (Alonso) is the most difficult driver I have come up against. Lewis Hamilton has also been a strong competitor as have Kimi Raikkonen and Michael Schumacher."
Massa and Alonso, both 31, have been teammates since the Spaniard's move to Ferrari from Renault in 2010.
Two-time world champion Alonso is currently leading the driver's standings with 179 points, 37 ahead of second placed Hamilton (McLaren-Mercedes). Massa is 10th overall with 47 points.
The next Grand Prix is in Singapore September 23.