Montpellier sign Lions prop
Montpellier sign Lions propSHARE
Ackerman, 25, joins from South African side Golden Lions to fill in for Guillamon, who is expected to be sidelined for between six weeks and three months following a groin operation.
Ackerman could make his debut away to Glasgow in the European Champions Cup on Friday.
Both sides lost their opening two matches and are in desperate need of a victory to retain any hope of reaching the quarterfinals.