Sub test()
Dim sh As Worksheet
Dim i As Integer
i = 0
For Each sh In Sheets()
If Val(Replace(sh.Name, "Ronde ", "")) > i Then i = Val(Replace(sh.Name, "Ronde", ""))
Next sh
ActiveWorkbook.Sheets.Add Before:=Worksheets(Worksheets.Count)
ActiveSheet.Name = "Ronde " & i + 1
End Sub