Roberto Martínez has poured scorn on Manchester United's attempt to sign Marouane Fellaini and Leighton Baines from Everton, suggesting it signals a departure from their transfer dealings under Sir Alex Ferguson.

United have not made a senior signing since Ferguson and the former chief executive David Gill were replaced by David Moyes and Ed Woodward respectively, but last week made what Everton described as "a derisory and insulting" £28m joint bid for Baines and Fellaini. The offer, submitted by Woodward, valued Baines at £12m, the sum Everton rejected in July, and Fellaini at £16m, less than Moyes paid for the midfielder five years ago, and it left Everton's chairman, Bill Kenwright, "angry, disappointed and hurt", according to Martínez.

The Premier League champions are expected to return with improved offers for the Everton duo and Martínez admitted he cannot guarantee the players will be at Goodison Park when the transfer window closes. But he insisted Everton have no desire to sell and have been left perplexed at United's transfer strategy.

"I have never seen Manchester United working in this manner before," the Everton manager said. "When you want a player you just do the business quietly, you get it done and that's it. I don't know if this is a new way of working at United. I don't expect a new bid. In fact, it wasn't even a bid because it never reached any sort of valuation of the players.

"There isn't an offer on the table where anyone would consider anything. If they'd matched the valuation maybe then you would listen to it but that hasn't been the situation."

Martínez claimed United's offer for Fellaini, who had a £23.5m buyout clause until 31 July but attracted no offers in that period, lacked common sense. He said: "If you invest a certain amount in a player and that player is one of the outstanding performers in the league, then I'm sure that price has gone up. It is common sense, isn't it?

"The market brings the valuation. There are aspects to consider like the age of the player and the length of his contract, but then it is very easy to look at the current price of that type of player in the market. That gives you a valuation.

"But I am not trying to fix a price for a player. It would be wrong to say that. I don't want to sell. But what is clear is if you want to buy a player and he's been a good performer, you must offer a higher value than what the club invested to get him. That's common sense."

Everton have received no fresh offers since rejecting the joint bid out of hand last Thursday and Martínez insisted Baines and Fellaini remain committed to the club. "So far everyone has been in a great frame of mind," he said. "They are focused, they are top professionals, it is their job and at the end of the day it is their passion. You can imagine it is not a fair situation for anyone."

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But the Everton manager conceded there are no guarantees over their futures with the transfer window still open. "Nobody can guarantee a player will be here on 3 September, in the same way you can't guarantee you'll have a squad that is fully fit," Martínez added. "If I guaranteed now they will stay I would be lying because if Real Madrid decides to give us €100m for a player I am sure we will not be able to stop that. I think we need to be realistic.

"I don't want to lose anyone and financially the club does not have to sell, which is very important."