The Hoops signed midfielder Stuart Armstrong and winger Gary Mackay-Steven from the Taysiders in January but the combined fee of around £2m was not enough to prevent some rancour between the United support and the board.
It has now been claimed that Celtic are considering going back to United for 18-year-old defender Souttar and 23-year-old striker Ciftci.
However, Deila, speaking at his press conference ahead of Friday’s home game against Dundee, said: “It is just rumours, I don’t want to comment on any names.
“We have our targets, we work on things, and when it is clear we will tell you. I can understand they are upset but they have to see it as a big honour that they are producing players that other clubs want.
“And if there are more players that we want, or anybody else wants, new stars will again come in their clubs. It is always tough for smaller clubs to lose players but they also bring a lot of money into the club.
“They can reinvest and build the club further and the small clubs need to do that more than the bigger clubs. But we also do the same, so every club has that decision to make.”
Asked directly about United perhaps being under pressure not to sell to Celtic again, the former Stromsgodset boss replied: “It is up to them.
“I think they know what price they want for the players and they have to think if they need money or not. But I don’t think too much about that.”
Celtic are eight points clear of Aberdeen at the top of the Scottish Premiership table and will clinch their fourth successive title if they beat Dundee and the Dons fail to beat United on Saturday, by which time Deila will be back in Norway for the confirmation of his twin teenage daughters.
“I am going to have a confirmation with my kids,” he said. “I am happy for the fixtures, that we are playing Friday.
“I didn’t think I could make it but now I can go home to Norway on Saturday morning to be there when they are confirmed. I will be back on Monday.”
Deila admits it will be a pity if Celtic fans are not allowed to celebrate a title win while actually at a match but insists the important thing is to get the league won.
“If we win and Aberdeen lose points then we will win it on the Saturday. But that (winning) is the most important thing,” he said.
“It is a very important game on Friday and I hope that we make it a big occasion and a memorable night. We will do everything to prepare ourselves to have a really good performance as it is a very important game to finish this off.”
Watch Celtic v Dundee live on Sky Sports 5 at 7.45pm on Friday.