It is not known how many players are affected.
General manager Greg O’Brien told Stuff they would not be identifying the players involved.
The news comes as the team announced five changes to their starting line-up for Friday's match against the Blues in Auckland.
The backline receives a shake-up, as Mosese Dawai comes in on the wing for Sam Gilbert, while Scott Gregory slots in at centre in place of Fetuli Paea.
Aaron Smith also regains the No 9 jersey, after Folau Fakatava stepped in during the 21-14 loss to the Hurricanes last Saturday.
In the forwards lock Manaaki Selby-Rickit switches back into the starting line-up, in place of Bryn Evans.
Marino Mikaele-Tu'u comes in at No 8, while Gareth Evans moves to the openside flank in place of Hugh Renton.
Highlanders team to play the Blues
Connor Garden-Bachop, Liam Coombes-Fabling, Ngane Punivai, Thomas Umaga-Jensen, Mosese Dawai, Mitch Hunt, Aaron Smith, Marino Mikaele-Tu'u, Gareth Evans, Shannon Frizell, Manaaki Selby-Rickit, Josh Dickson, Jermaine Ainsley, Liam Coltman, Ethan de Groot. Reserves: Rhys Marshall, Daniel Lienert-Brown, Josh Hohneck, Bryn Evans, Hugh Renton, Folau Fakatava, Marty Banks, Scott Gregory.
