Allen left the Liberty Stadium in a £15million summer switch to join the Reds, with Swans boss Michael Laudrup opting to bring in Ki from Celtic as a replacement for the Wales international.
Allen started his career on Merseyside with a string of bright performances but has come in for criticism in recent weeks, and has largely been reduced to a bench role.
Ki, meanwhile, has slotted in effortlessly alongside Leon Britton and Jonathan de Guzman in Laudrup's preferred midfield trio.
But, whatever flak Allen has had to take, Ki is in no doubt about the 22-year-old's class, and admits he has found it difficult to replace a player who was such a firm fans' favourite in south Wales.
"Joe is a very good player. I had watched him many times when he was at Swansea and I played against him in the Olympics too," Ki said.
"He can pass, he can do the defensive work very well and he just knows how to play football.
"Sometimes people expect you to be better than Joe was when he was here, but I respect him too much to think like that. He is a good player in his own right with great qualities.
"We are different kinds of players. I am obviously bigger than him and we have different aspects to our game, but we are also similar in our way of thinking about the game and wanting to pass the ball.
"He is a very good player and hopefully I can show I am a good player here too."
While Ki is looking forward to facing Allen, the fixture will also bring Ashley Williams and Luis Suarez into combat.
Williams courted controversy before the sides met at the Liberty Stadium earlier this season by being heavily critical of the Uruguay striker in his book 'My Premier League Diary'.
And the Wales captain knows Suarez will be the man to stop if Swansea are to get a result.
"He's going to start. He's a good player and they've got Daniel Sturridge as well, so it's going to be very tough for us defensively," he said.
"I haven't thought too much about facing Suarez again. We've just enjoyed a good win over QPR and we have done our work during the week for this game against Liverpool."