Xhaka was a major target for Chelsea manager Xabi Alonso after the Spaniard arrived at Stamford Bridge, with the pair having worked together during Bayer Leverkusen's unbeaten Bundesliga title-winning campaign.
Sunderland refused to sanction the move, keeping the 34-year-old on Wearside. His performances have since attracted scrutiny, with the Black Cats struggling to reproduce the form that helped them secure Europa League qualification last season.
Asked whether the transfer episode had left Xhaka dealing with a hangover, Le Bris admitted the situation was difficult to assess.
"[It's] hard to say. It's always complex. It's one element in the equation, so I don't know, to be fair."
The Sunderland manager was nevertheless emphatic about what he sees from Xhaka every day.
"What I know is what I see every day, the involvement of Granit, his standards, training standards, his willingness to play for Sunderland.
"Thursday, we planned to play 60 minutes, but at half-time he told me, 'I'll go all the way. I will help the squad.' This is Granit.
"So after that, he is human, he will have ups and downs. You are not the same player when you are 34 that you were at 23. His game is evolving as well, but his commitment is superb, no doubt about that."
Alonso declined to discuss his pursuit of the midfielder but made clear the importance Xhaka had played in their successful partnership at Leverkusen.
"We spoke a lot in that time in Leverkusen with Granit because he was a key part of that team.
"He glued many, many pieces together in the middle with the back three. Mostly with the players around him. It was a very good time together and I'm looking forward to seeing him on Sunday."
Sunderland defender Trai Hume also rejected suggestions that the transfer speculation had unsettled the dressing room.
"No, it's had no effect on us as players. Granit has obviously been a big player for the club since he's come. He's our captain, our leader, and just like us, he knows he can be better and we know we can be.
"He demands more from us. We need to step up to the levels we know we can hit but haven't reached this season. We know as players we are a good team and we have to reach the levels of the Premier League.
"Unfortunately we haven't reached that so far but that's what we need to address and improve."