It looks like Bayer Leverkusen already has very great players this season. If Bayer Leverkusen wants to use the funds collected to buy new players, it will further increase the burden of salary costs for the players every month. It is better to save the funds that Bayer Leverkusen has, and if you want to buy New players must wait for the number of players they have to decrease first so that the amount they spend each month is still balanced and will not create financial chaos at Bayer Leverkusen.
Xabi Alonso will never forgive himself if his outstanding team doesn't end up winning the Bundesliga title at the end of the day, because he has been patient all this while and have become one of the very confident coach to go home with one of these major trophy. Leverkusen in good touch and om streak winning, unbeaten in all Bundesliga matches played and they will continue from where they stop after the christmas break. At this current moment, Bayer Leverkusen doesn't need any new player or new strategy to ruin their chances of winning the Bundesliga title this season.
I think you are underestimating the other teams in the Bundesliga, so Bayern Leverkusen does not need new players for the rest of the league, we know that the January market is eagerly awaited by many teams to get the players they want to get additional strength, often they are burdened by the cost, but it is worth the price to get potential players and strengthen them until the end of the league.
So I think Xabi needs new players and some players who do not have above average abilities need to be sold, Xabi Alonso needs to anticipate the developments that may be brought by Bayern Munich, Leipzig, Dortmund and other teams will add to their strength. So I don't think Xabi will take any chances in the next month's market.