Ryan not only played for the two teams but coached and managed them as well, famously stepping in to Sir Alex Ferguson's shoes for the game against Middlesbrough in 1998 and having a long and distinguished spell involved with the Reds' superb youth system.
He also managed Luton in the early 1990s, staving off relegation from the top flight, before switching to United.
Erik ten Hag's team approach Sunday's 16:30 GMT kick-off in good heart after four successive wins in all competitions but will be tested by a Hatters outfit that have surprised a lot of people this term.