Evans signed a one-year deal with Manchester United after being released by Leicester City last summer.
"Jonny and I have a really good relationship and we have had those conversations (about retirement)," O'Neill said.
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"I'll obviously try and talk him out of that scenario (retiring from football) but we'll obviously respect whatever decision Jonny makes.
"He has been a great player for me, he's been a great player for Northern Ireland, but I think he's still got a few miles in the tank yet.
"He brings a lot. He's not going to go out every week and play in the Premier League, but at a club like Manchester United where there is European competitions and cup football I think he's more than a useful player to keep around."