The 26-year-old injured the knee in training on Monday and a MRI scan confirmed an Anterior Cruciate Ligament (ACL) tear.
New Lions head coach Swys de Bruin confirmed that Skosan will be sidelined for the entire tournament.
“It’s going to be about six months out for him,” he told IOL.
“It’s a big blow. It happened in a freak accident in training on Monday... and it wasn’t even a contact session. He just ran into another guy. It’s a huge setback, but we’re at least well covered on the wing.”
Skosan was in fine form for the Johannesburg-based outfit during 2017 and was called up to the Springbok squad.
He represented South Africa in 12 Tests in 2017 and scored two tries.
The Lions will play the Bulls in a pre-season match on Saturday at Ellis Park (15:00) and open their Super Rugby campaign against the Sharks, also at Ellis Park, on Saturday, February 17 at 17:15.
Lions team to face the Bulls:
15 Gianni Lombard, 14 Madosh Tambwe, 13 Manuel Rass, 12 Howard Mnisi (captain), 11 Aphiwe Dyantyi, 10 Ashlon Davids, 9 Marco Jansen van Vuren, 8 Willie Engelbrecht, 7 Hacjivah Dayimani, 6 Marnus Schoeman, 5 Marvin Orie, 4 PJ Steenkamp, 3 Jacobie Adriaanse, 2 Corne Fourie, 1 Sti SitholeSubstitutes: 16 Pieter Jansen, 17 Cohen Kiewiet, 18 Jo-Hanko de Villiers, 19 James Venter, 20 Len Massyn, 21 Christiaan Meyer, 22 Shaun Reynolds, 23 Louritz van der Schyff, 24 Wandisile Simelane