Rovers lie just three points above the relegation zone as they prepare to host Huddersfield at Prenton Park on Saturday.
Les Parry`s men currently lie on 43 points and McChrystal, who is aiming to shake off a hamstring strain and be passed fit for the weekend, is wary about the threat of the drop.
He said: "You have to expect the teams below us to start making a fight of it. Everyone is scrapping now there are less than 10 games to go.
"We've spoken about targets with the gaffer and we reckon around the 50 mark - although the way things are going we may need a few more points than that."