The 22-year-old sustained the injury during the first half of Sheffield United’s 3-2 Premier League defeat by Manchester United last week.
“Sander Berge had an operation on his tendon in his leg, so it’s obviously a huge blow for us with him being out between three and four months,” Wilder told reporters.
Wilder said he does not expect midfielder John Lundstram, who can fill in for Berge, to leave the club before the English player’s contract expires at the end of the season.
Lundstram will be unavailable for their next three games starting with yesterday’s visit of fourth-placed Everton, having been sent off for an infraction in last Sunday’s 1-1 draw at Brighton & Hove Albion.