Valencia CF are unlikely to bring in reinforcements this winter transfer window as the club is saving up money for salaries and the possible restart of construction of the new Mestalla. As you all know the club sold most of its key players this summer and kept a small core of players. This brought a decent amount of needed cash and lowered the salary bill significantly, but it also meant rebuilding the team yet again anew with a new coach on top of it.
Valencia CF brought in new mostly loan players and older players in order to fill up the team and tasked Gennaro Gattuso with forging this new team. The team is likely self-sufficient right now as in it probably brings in enough revenue and has low enough expenditures that its likely making small profits at the end of the season, though that is without actual transfers.
In order for the club to bring in new players it would have to first sell players and then use that money to bring new players. So, you can see how the club is unwilling to spend any money in this transfer window and is keeping its options for summer.
There has also been limited speculation, with few reports suggesting that Valencia CF might bring in a midfielder and one winger, but even in the speculation department it's been fairly quiet, this just goes to show how unlikely it is for Valencia to bring in any new players.
I think the current squad can improve slightly and bring in somewhat better results, but it's going to take very hard work and a serious dedication by the players to want to do much better.