Lewis Hamilton admitted he endured a difficult afternoon at the Spanish Grand Prix as he slipped to twelfth place.
Hamilton suffered from tyre degradation and vented his frustration to his team via the radio, saying 'I've just been passed by a Williams' and 'I can't go any slower!'
The Brit was forced to convert to a four-stop strategy during the race but could only finish twelfth, one lap behind winner Fernando Alonso.
"A difficult afternoon today and going backwards is never fun. We switched to a four-stop strategy during the race but I suffered with a lack of grip and balance throughout and we were never really able to get the tyres working."
"I know that everyone at the team is working so hard and we need to keep positive. I'm sure we will figure the problem out and we've got to keep pushing together to close the gap. I will be doing my best to help and encourage the guys," he added.
Spain marked Hamilton's worst result of his Mercedes career.
Team principal Ross Brawn also expressed his disappointed and admits the race pace of the W04 needs urgent attention.
""We endured a very difficult afternoon and the comparison between our competitiveness in qualifying and in the race was particularly disappointing. Nico [Rosberg] did an excellent job managing the tyres to make just three stops and his level of performance showed what our car is currently capable of on tracks like this."
"Lewis didn't have a good balance at any point and that simply made a critical situation worse, which forced him to convert to a four-stop strategy midway through the race. We must find the key to why we are losing performance on Sunday afternoon and find the right solutions to improve."