Collins was making his comeback from a groin problem when a Pompey player appeared to fall on his leg following a 50-50 challenge.
The Welsh international left the ground on crutches and is expected to have further scans on the knee today that may indicate ligament damage.
Danny Gabbidon told the official site, "You are hoping everyone gets through the game and no one gets injured.
"I feel for James because he was playing really well up to then. He was a bit unlucky the guy fell on his knee and he has done something to it. Hopefully he can recover and get back as quick as possible. It is disappointing to see him get an injury."