Two-time Le Mans winner Allan McNish admits that Audi was taken by surprise by Toyota's competitive showing last year.
The Scot reckons improvements are now needed for Audi to stay ahead of its Japanese rival. Audi took overall honors in the World Endurance Championship last year after contesting all eight rounds.
Toyota began its campaign at the Le Mans 24 Hours, where it led, and won at Interlagos in September.
McNish, who finished second in the drivers' championship, confessed at AUTOSPORT International that Toyota's competitiveness toward the end of 2012 – when it scored three wins from six races – came as a shock.
"We were surprised by their consistency of pace," said the Scot. "They were quick at Le Mans – they were quicker than we expected – and when we got to the other races they were good every weekend. They definitely made us sit up and think."
He felt Toyota had given Audi a fresh impetus to succeed.
"They have given us ideas on where we need to improve performance over the winter and we've been doing that pretty intensively," McNish said. "Audi has been in it for a long time and are definitely the benchmark. Saying that, you can always learn from the opposition.
"It's going to be tough. They're going to be good. But then again, they have to be good if they are going to beat us."