Many Kilmarnock fans were disappointed to see their top goalscorer for the past two seasons leave on the eve of their 2-1 Scottish Premiership defeat by Motherwell at Fir Park.
But Johnston hinted that the Irishman's agent had been seeking a new club for the forward for several months.
Johnston, whose team failed to build on a 17th-minute lead at Fir Park, said: "Heff's a good lad but he wasn't too happy playing up front with Boydy (Kris Boyd) as well and I think he wanted to leave.
"If he wants to leave then it's better for us if he moves. It frees up a lot of money because he was probably the top-paid player at the club.
"So we should hopefully be able to bring in a couple of players.
"He never asked to leave but his agent said Hibs and Motherwell were interested in him at the start of the season and that just came about again."
Killie only held the lead for three minutes when Henri Anier levelled after Stephen McManus had put through his own net, and a fresh-air swipe from Jackson Irvine allowed John Sutton to net on the stroke of half-time.
Johnston said: "You can't afford to defend the way we are defending and win games. We are making it an uphill battle week in and week out.
"I thought we played really well. I thought we dominated, especially the second half, passed the ball really well and looked really confident, and you can see we are not far away."
Motherwell manager Stuart McCall admitted Ramsden had been "rash" in challenging Rabui Ibrahim for the late tackle that earned him a second booking following a yellow card for dissent.
And he praised Hollis, who was handed the gloves at the start of the season despite the signing of Gunnar Nielsen.
"Lee Hollis has made two fantastic saves," McCall said. "It doesn't matter how you keep them out, one came off his knee and one came off his heel, and over the piece I think we did deserve to win.
"Lee has not had a great deal to do in the games we have had of late but today when he was called upon he made some crucial saves.
"That's what he is there for. He is getting pushed all the way by Gunnar. They both train ever so well and push each other. You need good competition all over the park and we have certainly got that in goal."
McCall finished his transfer business with the loan signing of Lionel Ainsworth on Thursday but Johnston will try to bring in two free agents after the transfer window shuts.
Johnston said: "Hopefully with the money we have saved with Heff moving on, we should be able to strengthen.
"We have been trying to bring in a centre-half and a couple of them fell through that we tried to bring in on loan. There are a lot of players available and I still think we need to bring in another two."
- Sports & Recreation