Cluch problem with Vauxhall Vectra dTi 2.0

I have vausxhall vectra, dTi, 2.0 The gear engages normally when engine is cool. However if engine is hot example when stuck in traffic or after long drive in minor roads, engaging the gears becomes really hard. And at times I have to pump the cluch twice or more to get the gear engaged. I opened the window to hear the cluch when pressed down, and i heard the cluctch makes squeaking noice when pressed. Any answer please?