Athletic Club is a great team and they will want to beat Barcelona at the end of this season. Barcelona have already secured their trophy in La Liga and they will want to continue their winning streak. Accordingly, they may not field a team with second-tier players. I think Barca will play with their full strength and will try to beat Athletic Club. We can say for sure that it will be an exciting match between both the teams and Barca will have a higher chance of winning. Although Barca is ahead in the win statistics of these two teams the win or loss depends on the best performance on the specific day to get the win.
Yes, Bilbao are in serious form, and that is the reason they are occupying 4th position in the table currently. So, even though this match is important to Barcelona, it is not going to be an easy match for them against team like bilbao. But now that the match is not important to Barcelona and it is important to Bilbao, I will say that Bilbao is the favourite team to win the game. They are fighting for 4th position on the table to be able to qualify for next season Champions League.
I know that Bilbao will likely do everything possible to win the game or at least draw, because even a draw can make them qualify for next season Champions League. Currently, Bilbao are at 70 points and Villarreal are on 67 points, so even with a draw, Bilbao will be leading by 1 point.
From my observation, it is possible that Barcelona may use their first squad, but they might not put in full energy to play the match, as they have already won the La Liga trophy. It is also possible that they won’t use their full squad, and if that is the case, I will say that it makes the match easier for Bilbao. But let’s see what will happen, as football is unpredictable.