diff --git a/tournaments/forms.py b/tournaments/forms.py
index 7ea066b..db57a06 100644
--- a/tournaments/forms.py
+++ b/tournaments/forms.py
@@ -56,6 +56,12 @@ class TournamentRegistrationForm(forms.Form):
 
     def clean_mobile_number(self):
         mobile_number = self.cleaned_data.get('mobile_number')
+        if mobile_number:
+            # Basic regex for mobile numbers, matching common formats
+            # Remove spaces from the number first
+            mobile_number = mobile_number.replace(' ', '')
+            if not re.match(r"^\+?\d{10,15}$", mobile_number):
+                raise forms.ValidationError("Entrer un numéro de téléphone valide.")
         return mobile_number
 
 class AddPlayerForm(forms.Form):