Portsmouth have confirmed the signing of former Manchester City midfielder Kelvin Etuhu on a free transfer.
Etuhu, 23, has been without a club since leaving City after serving a prison term for assault. He has been training at Pompey for two months.
"We are delighted to bring Kelvin on board," Appleton told BBC Radio Solent.
"He has been training with us for two-and-a-half months now but we've had to keep it very quiet. We didn't want to lose out to someone else."
Etuhu has Championship experience having had loan spells at Cardiff City and Leicester City while he has also played in the Premier League with Manchester City.
And Appleton believes his previous misdemeanours will make Etuhu more hungry to succeed with Pompey.
"I am very aware of how hard he has been working," added Appleton.
"He has come in off his own back and trained very hard every day and we have not paid him a penny. He wanted to improve and because he has been training with us for two months he should slot straight in.
"I was aware of Kelvin as a young lad at Manchester City and have seen him play a few times and he has Championship experience.
"He is so desperate to be successful because of what has happened to him in the past and sometimes young players can use a bad thing to happen in there life as a positive.
"He is a very polite chap and we are looking forward to him playing and he goes straight into the squad for Saturday."