The Tynecastle Park manager expects to sign at least one more new recruit before the end of the month following the capture of Australian defender Nathaniel Atkinson.
The principal target is now a forward to help ease some of the pressure on top goalscorer Liam Boyce, who struggled with a calf injury prior to the Premiership’s winter break.
Potential Covid infections remain a concern for all clubs and Neilson told the Evening News that he wants to run with 18 outfield players in the first-team squad.
Ken Buchanan: Statue of Scottish boxing legend unveiled on Edinburghs’s Leith Walk
Robbie Neilson reveals Hearts' chances of a new signing for Zurich tie - plus Alex Cochrane and Craig Halkett injury update
Hibs debrief: Alarm bells in the stand (and defence); Tavares decision; ref's big calls
Former Hearts striker steps out of 'comfort zone' with move to Turkish top flight
How the Hearts players rated in the 4-1 victory over Dundee United
Asked if he planned to increase numbers in case of a virus outbreak, he replied: “No, not really. We will maybe add one more to the squad. We have 17 outfield players and we expect to run with 18 altogether if we can get the right numbers in.
“You always need to try to make sure you come out of the transfer window stronger than when you went into it. You also need numbers at the same time. If anybody is leaving Hearts then there will be people coming in to replace them because we do need numbers.
“As we have all seen over the last couple of months with a number of different teams, you get a Covid outbreak in your squad and you can be struggling to put a team together. That means we need to carry a decent-sized squad going into the run-in.”
Jamie Walker left Tynecastle to join Bradford City on loan this week, with Armand Gnanduillet also expected to return to England before the window ends.