There have been concerns Messi is not fully fit after picking up a thigh injury against Valencia at the start of February, but Valverde said in a pre-match press conference he's happy with his captain.
"I think he is in good shape, very good shape. You always expect a lot of your players, Messi included," he said. "He always performs, even though in some games he performs less than in others. We have to play well in order for him to perform."
Saturday's match between the two fierce rivals is the second Clasico in the space of four days at the Bernabeu.
Barcelona won 3-0 on Wednesday to secure a 4-1 aggregate victory and reach the final of the Copa del Rey.
Messi had a quiet game by his high standards, as Barca progressed with Ousmane Dembele supplying two assists, Luis Suarez scoring a brace and Raphael Varane handing the visitors an own goal.
ESPN FC's Samuel Marsden noted Messi's record at Real Madrid:
According to Moises Llorens at AS, Messi is "tired and lacking power" but is keen to play well against Real Madrid because "he owes Barcelona a massive game in the Clasico."
Victory for Barcelona on Saturday would see them move 12 points ahead of Real Madrid in the table and effectively end their already slim hopes of winning the league title.
Valverde's side will be confident after their 3-0 victory on Wednesday, and they also boast an enviable record at the Bernabeu:
Messi may not have scored in midweek but he's enjoyed another brilliant season:
1 - Lionel Messi is the player from the top five European leagues with the most goals scored in: ✅ Year 2019 - 10 ✅ 2019 (all comps) - 12 ✅ Season 2018/19 - 25 ✅ 2018/19 (all comps) – 33 ❌ 2018: 34 ✅ 2018 (all comps) – 47 ✅ 2017/18 - 34 ✅ 2017/18 (all comp) - 45 ... https://t.co/wuQ3mC8M3c
The Argentine and Barcelona were not at their best on Wednesday despite running out 3-0 winners. However, if they can produce an improved showing on Saturday they look likely to secure a third win over Real Madrid this season.