The Jambos manager is still hopeful the defender will decide to shun the interest from Rangers plus English duo Sheffield United and Blackburn Rovers to stay at Tynecastle with his contract running out in the summer.
However Neilson is working with head of recruitment Joe Savage to ensure a contingency plan is in place should the defender move on – but insists he won’t allow a repeat of the ‘drift’ that overshadowed the club in 2016 when Osman Sow left early and before the end of his deal.
“I felt that had a real effect on the dressing room, the club and the fan base - we lost one of our key players,” Neilson said. “We ended up, although we finished third, we kind of drifted over the line that year.
“We have to keep our best players in the team and if they go at the end of the season, then the end of the season is when they go.
“Unless a crazy bid comes in, but I don’t expect one.”
Neilson’s desire to keep Souttar extends beyond the short-term, but if the defender remains only until May he can still help the club’s objective of European football.
“John is a top player and he will continue to play in the team and will continue to do well,” he told the Scarves around the Funnel podcast. “We will continue to take it game by game.
“We would love to keep John. We still hope he will make that decision to stay with us. Is he going to do it? I’m not sure.
“I know there have been a lot of suitors for him, as has been the case with a lot of our players.
“We are looking at centre halves just now and in the summer."
He went on: “I don’t think John has signed anything anywhere. I’d be surprised because there has been no contact made to us.
“It is the same as we have said all along, our aim is to get European qualification.
“So it is really important we keep the group together.”