Forum:Kaiser coliseum question

my opponent already has two monsters on the field when i activated kaiser coliseum. also i set a monster on my field. during my opponent's turn he tributed one of his monster to tribute summon a level 6 monster(eg: jinzo). is this allowed? i only have 1 monster on my side of the field, so he can't add another monster on his side of the field, and tributing monsters will remove it on the field, so he will automatically have 1 monster. can he still summon the level 6 monster? is this considered as replacing the tirbuted monster? thans a bunch!!