The Spanish playmaker was involved in both the European Championship and the London Olympics this summer and subsequently spent several weeks resting before returning to the Chelsea side.
Cech, who produced some crucial saves during the Blues' 4-2 win against Tottenham Hotspur on Saturday, feels the Spaniard has returned with boundless energy and enthusiasm.
"People were surprised when he left us after the start of the season and went for a holiday but you can't play two seasons in a row," Cech told the club's official website.
"By this time he would have been burnt out without any break, but now you can see he still has the hunger to play, and he is fit and has a lot of energy. It is great to see him playing like that."
Mata netted two crucial goals against Spurs, taking his tally to six in his last five appearances in all competitions. However, he is refusing to get ahead of himself, and insisted that the team are focused only on their next match.
"What we need to do is keep training hard and now we play Shakhtar Donetsk in Ukraine and we want to stay at the top of our group in the Champions League," he said.
"It is too early to think about winning the Premier League, it is our aim of course, but what we have to do is keep going and keep on enjoying ourselves."
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