Finland international Eremenko was paraded at Rugby Park at half-time during Saturday's 2-0 win over Inverness, a victory clinched after Boyd struck his 13th goal of the season.
But despite luring him to Scotland for talks, boss Johnston says he is unsure if a deal for the 30-year-old playmaker - who struck four goals during a year-long stint with the Ayrshiremen in 2010-11 - can be struck.
"I don't know how close we are yet but I will speak to Alexei later today," said the Killie boss after watching his side move up to eighth in the Scottish Premiership standings.
"Obviously we are interested in quality players and it would be great to get him here.
"Time will tell whether we can afford him but it is a positive that we have got him here to talk. It doesn't guarantee anything so we will have to wait and see."
With six days left of the January transfer window, though, it is the thought of seeing top-scorer Boyd leave that is currently giving Johnston palpitations.
It was a result richly deserved - Killie's first over a top-six opponent this season - but Johnston now has a week of worry ahead of him before the transfer deadline passes.
"It was a real team performance but there was also some really good individual performances," he added.
"Robbie Muirhead was great, while young Gregg Kiltie was fantastic too starting his first game. He took the ball in tight spaces and was never afraid to play a pass.
"The young players did so well but without the experience of Boydy and Sammy Clingan that result wouldn't have been possible.
"We cannot afford to lose somebody like Boydy. He is too big a player for us with his goals."
Inverness boss John Hughes has now lost four out of his nine games in charge since replacing Terry Butcher and admitted his tactics at Rugby Park were too open.
He said: "We lacked a little bit of imagination to break them down but you have to give them credit for that. Our effort and commitment was absolutely fantastic.
"However, we need to be a little bit more streetwise. Their second goal came just as we were getting back on top. We were going for it and if I had to go to one at the back I would do it.
"When we were pushing I thought that they might pick our pocket and that's what happened - but it won't happen again.
"You learn from it and this might be the best thing that's happened to us. Even in defeat you'll never hear me criticise these Inverness boys.
"But sometimes you have to take one on the chin to come back as a better team. I think that might just be the case today."