Lacazette has started 13 of Arsenals 20 league matches this term and completed 90 minutes in just seven of his appearances.
Emery has favoured Pierre-Emerick Aubameyang in a central role and Arsenal fans booed the Spaniards decision to take the Frenchman off in their 4-1 win against Fulham on New Years Eve.
Pires, though, insists Lacazette has to start when available and says the striker is a perfect fit for the Gunners.
He is a good point of support & his performances are always good, said Pires.
The good thing with Alex is he never seems in doubt. He knows his strengths & qualities. Also, he completely matches our game.
If he is always available, he has to play. Its simple.
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Emery hit back at supporters for booing his decision to substitute Lacazette, insisting he has to make difficult decisions.
I understand the supporters but I need to do my work, said Emery in his post-match press conference.
Tactically in this moment [midway through the second half] we are thinking to change to get more balance.
We know very well that Seri is coming and we need to have one more player closer to him, not to let him play with the ball easily and I think when Ramsey is on the pitch he can do that but also help us in the attacking moment.
This reason is this, I need to do my work and not because some supporters think different opinions.