Madrid - Barcelona gave Real Madrid the chance to go top of La Liga ahead of Wednesday's Clasico at Camp Nou as they were held to a 2-2 draw by high-flying Real Sociedad on Saturday.
Madrid will pull two points clear at the top of the table if they win away at in-form Valencia on Sunday, which could prove a significant psychological boost ahead of their crunch meeting with Barcelona in midweek.
"The game has a special meaning but there are some things we need to improve."
Two tight penalty calls also went Real Sociedad's way as they got one for a shirt-pull by Sergio Busquets and got with away another as Gerard Pique went down at the back post late on.
"Now he is playing regularly you can see what a player he is," Valverde said.
The home goal though came from a corner as Busquets was spotted tugging Diego Llorente's shirt.
The visitors improved after half-time and were ahead within four minutes of the restart. Busquets clipped a ball over the top of Llorente, who stepped up at the wrong time, allowing Lionel Messi to skip free.
Instead Real Sociedad levelled. Monreal's cross caused panic and Ter Stegen parried the ball straight to Isak, who had a simple finish five yards out.