Keeley turned down a new Spurs contract offer this summer to join Luton Town last week.
Attacking talent Melia, 17, will leave St Patrick's Athletic for Spurs when he turns 18 years of age.
Keeley said, "I mean he is a young lad, who has played a lot of senior games at the minute and he is playing constantly for St Pats. I think him coming over, signing for Spurs and getting to know all the boys is only going to help him progress.
"He is going to do very, very well."
On his decision to join League One Luton, Keeley also told football.london: "I mean I’ve been around London quite a lot on my loan spells (at Barnet and Orient) and because I have got some family in London as well, I think it’s important to stay close and connected.
"I spoke with Dean Brill, he played here as well and he sold it to me. He told me it was a great club and the people here are very good people.
"I think the club has very high expectations. Being a Premier League club, we have got every aim of getting promoted to the Championship first and then after that we can worry about going up again. This season is important. It starts now, everyone is looking forward to it and hopefully we can push for promotion."