The Scot was among the star men on an impressive outing for Wednesday, who finished the season in fourth place and are set to play Sunderland in the playoff semi-finals.
The first leg of that clash will be played on Friday and with only six days to recover, a packed-out Hillsborough fell near-silent when Bannan went down holding the back of his leg with only a few minutes remaining.
Bannan took part in the player’s ‘lap of honour’ after the match and seemed to be moving relatively well as he left the ground.
Wednesday boss Darren Moore said the club would have to wait to get any sort of prognosis on any lay-off.
“The news that I can give to everybody is that he’s been with the medical team but we always like to give it 24 or 48 hours to let it settle down,” he said.
“Sometimes you can make decisions too soon. We always give it 24 or 48 hours and then you get more of a clear picture. That’s what I want to do over the next couple of days to see how he is.
Asked how concerned he was over the potential issue, Moore said: “What’s the point in worrying now?
“We don’t know what’s going to happen and we might be jumping to conclusions. In a couple of days things can settle down and we’ll be able to give you a better idea.”
On an impressive performance in which the Owls had to come from behind, Moore said: “It was all about coming here today and getting the job done. We had a strong opposition up against us today and I thought once we settled down a bit we got into a rhythm and played some good stuff.
“The strength of character to go a goal down and not lose sight of the process, keeping to the gameplan, we saw clear pictures and the areas we wanted to exploit Portsmouth. We got the goals.
“It could have been very difficult but we got stuck to the task and came through it together.”