Navjot Sidhu, who played a big role in the two-time Punjab Chief Minister Amarinder Singh's abrupt exit, also stunned the party by resigning as Punjab Congress chief on Tuesday. "Sidhu is an immature person. I have said this repeatedly that he is not a stable man. He is not a team player. He is a loner. How will he handle the Punjab Congress as its chief? For that you need to be a team player, which Sidhu is not," Mr Singh said.