Mercedes boss Toto Wolff has claimed that the constructors' champions will be keeping an eye on Ferrari because the Italian team has "come alive" in recent races.
The Scuderia took their third victory of the season as Sebastian Vettel won the Singapore Grand Prix last weekend.
However, while Wolff has suggested his team will be paying closer attention to Ferrari, he is confident that the characteristics of Suzuka will suit Mercedes more.
He told Sky Sports News: "You always have to look at them – and also Red Bull made a step forward. They are strong competitors and you cannot expect or take it for granted that you are always quickest and always winning races.
"This is not normal for Formula One so we are going to have an eye on them. This circuit should certainly suit us much more than Singapore but certainly the enemy has come alive!
"I think in particular the last one was a surprise because the way they won it, complete domination. But everyone is keen to see good competition in Formula One and especially Ferrari, such an iconic brand, to see them bouncing back is good for the sport and good for us to have a strong competitor, it makes it more precious to win."
Toro Rosso's Carlos Sainz Jr topped the timesheets in first practice at the Japanese Grand Prix before Red Bull rookie Daniil Kvyat finished fastest in FP2.
