Wissa opened the scoring in their 2-1 defeat at Manchester City, but was forced off before halftime.
Frank stated: "It could be a shorter one or it could be a longer one, I actually have no clue. We need to assess him tomorrow.
"It was a reckless tackle, I thought, from Kovačić, just going through the man, from behind him.
"I know it's probably not a red card, but it's frustrating that it's led to an injury."
Frank added: “50 per cent of me is very frustrated we didn’t get something out of the game; 50 per cent is extremely proud of the team, the players and the club.
“The performance today was, overall, much, much better than two years ago.
“The first 25 minutes we were close to world class… not many teams come here and have more possession, shots on target, xG.
“Second half they got a little bit more on top, but we stayed in the game and had two opportunities.
"The fans should be very proud."