In similar situations I will extract the lookup to a constant in the class, and use the String.format utility to insert the variable(s) where I need it. Note the use of %s in the example constant USER_XPATH below.
I think this is better for readability and maintenance than the inline concatenation option, but both will achieve the goal.
/** Format string for the ### xpath lookup.*/
private static final String USER_XPATH ="//td[normalize-space(text())=%s]/a";
Then you can use String.format to insert the variable you want:
private void myMethod() {
String newUser = "NewUser123";
String fullXpath = String.format(USER_XPATH, newUser);
driver.findElement(By.xpath(fullXpath)).click();
}