Peaking too early will only cost them if they get a fixture pile up, in th later rounds of the CL that would be a big possibility as English teams still in all 4 competitions in March/April end up playing far too much (thats why the treble was such an achievement
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In February though there wont be a fixture pile up, and Arsenal use their reserve side in the early rounds of the FA Cup and League Cup anyway so most of the players are quite well rested.