#1 - David De Gea
The Spanish shot-stopper is one of the world's best keepers in the world and has been United's best player for the last 4 years, making him their most prized asset. De Gea was all set to leave United for Real Madrid back in 2015 only for the move to fall through due to botched paperwork, on the last day of the transfer window.
De Gea is fundamental to United's bid for the title and losing him, especially on a free transfer would be a major blow to Jose Mourinho. The Spaniard endured a horrible world cup, managing just one save the entire tournament. De Gea's current contract turns up to 2019. But United are understood to be relaxed and expect De Gea to put pen on paper on a new long-term lucrative deal, that would keep him at Old Trafford in his prime.