The Mercedes Formula 1 team relaxed too much after a dominant 2014 season, according to former world champion Jacques Villeneuve.
Mercedes has won three of the first four races of the season, but was beaten on pure pace by Ferrari in Malaysia and was again under threat by the Italian squad in the last race in Bahrain.
The German squad won 16 of the 19 races of the 2014 season, and Villeneuve reckons the team did not expect anything would be able to catch up at the start of 2015.
"It seems that, having achieved success, the team (Mercedes) relaxed a little bit," Villeneuve told France's Auto Hebdo.
"I think Mercedes did not believe anyone could catch up with them, not realising that the situation had in fact changed."
World champion Lewis Hamilton is the runaway championship leader after the first four races, with three victories and four pole positions so far.
The Briton has dominated teammate Nico Rosberg so far, and Villeneuve believes the German driver needs to return to winning ways quickly in order to regain the confidence that helped him take the championship battle to the wire in 2014.
"Victory would help him return to his previous form, so Nico needs to start winning as soon as possible," the Canadian added.