The Ireland Under-21 star has been captain all season long apart while Bullen has been out of the side because of injury and failing to hold down a first-team spot.
But many fans believe that the new responsibility has hampered Whelan's game but the youngster is not feeling the strain and admits that the captaincy is making him a better player.
"I don’t feel any pressure at the moment – it’s a game of football!" Whelan told Footymad.
"Obviously if we don’t win people can get on our backs but we are not going to win every game and just get on with it. I am not one of these people who will just give up though and hang my head if things are not going well.
"I know if I play badly at all I will keep my head down, work harder and do better the next game – that’s just the way I am. The gaffer and the management have said to me I have to be more vocal and I am doing that but I am really enjoying being captain at the moment."