Panathinaikos boss Rui Vitoria told his 'tired' players their pre-season defeat to Braga was a warning to raise their game for Rangers.
Rangers face the Greek side a week tomorrow in the second qualifying round of the Champions League at Ibrox before the return in Athens.
Panathinaikos faced the Portuguese side in a friendly in Kossen, Austria, before they play Rangers.
And Vitoria reckoned the defeat proved they have to improve ahead of playing Russell Martin's men.
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He said: "The positive thing is that we didn't get any injuries, so we have all the players at our disposal, so we can work together and focus on the matches against Rangers.
"We are not satisfied because we lost. I could say that this was a warning. It is not worth doing some things well and badly with other things. You have to be focused throughout the match.
"Braga didn't do anything special, yet we found ourselves behind and were always chasing the game.
"And mistakes cost us.
"What we need to do now is rest. We've been in Austria for two weeks with a lot of intensity.
"There is fatigue among the players, they are tired. We also had to manage a large volume of players in the squad and give them all game time."
