Park has had the 24 year-old watching on in awe.
"Ji is a fantastic player," Ephraim told the club's official website. "He's a class act - both on and off the pitch - and it was great to play in the centre with him.
"I've not really played there before to be honest. I've done it in a three, but not in a two, so I'm learning all the time and taking things on board as much as I can.
"The manager feels I can play there so I'll give it my best shot. Hopefully that continues and playing with people like Ji will only help.
"He's a quality player and being a United fan as well I've seen plenty of him over the years and know just how good a player he is."