Sitting on the verge of the play-offs and with one of the league's top goalscorers a key part of the first team would be absolutely fcuking crazy to sell that player for any amount of money in my opinion. They would need certifying if they were to sell that player to a rival team regardless of what colour shirt they wear.
And if a player, ANY PLAYER, tried to force a sideways move to a rival club then they would be sat in the reserves for the next few months until their contract expires. Not to punish the player but simply because if you lose a good player from your first team you have weakened your team, if you transfer them to a rival you have weakened your team AND boosted theirs. Dropping the player for 5 months is from an on pitch point of view significantly less damaging than handing him over to a rival.