Ronald Koeman is resigned to the departure of Morgan Schneiderlin before the start of the season though the Southampton manager has warned Manchester United the France international will not be signed on the cheap.

Schneiderlin, who was absent through illness at his club’s Staplewood training base on Monday but is due to travel with the squad for their get-together in Austria, was the subject of a £20m bid from United two weeks ago. That offer was rejected but Southampton, who are prepared to make a formal complaint to Fifa if Atlético Madrid sell Toby Alderweireld to Tottenham Hotspur, are prepared for a second bid.

United want to secure Schneiderlin before their tour to the United States and for which they depart on 13 July but will have to up their bid to nearer £27m to stand any chance of securing the 25-year-old midfielder. “Every player has his price and we have experience as a club of selling players,” Koeman said.

“Last season we sold some players, and if there is interest in Morgan then OK. But it has to be at the price the club wants. He is one of the key players or our team, an international player. And I don’t think is a problem for Manchester United.”

Asked if he was planning for the campaign ahead with Schneiderlin in the ranks, Koeman said: “No. I know the situation. I have spoken a lot with Morgan. Last season we finally said: ‘Stop all this business because we are not selling any more players’ [after Adam Lallana, Dejan Lovren and Rickie Lambert had been sold]. That was difficult for him but he came back after a few days with good motivation and had a great season. But we know the situation now. There is a lot of interest in the player. With a club like United, we know it’s difficult to keep the player. But if they pay, then OK, we can make the transfer.”

Koeman has already pinpointed the Feyenoord midfielder, Jordy Clasie, as a replacement for the Frenchman should agreement be struck with United. “He’s a good player, a young player and a Dutch international who is ready to make a step up and show his qualities at a higher level than we have in the Dutch league,” he said. “He’s growing in his leadership qualities too and, if Morgan goes, we’ll need a player in that position. He is one of them [on the list of potential replacements].”

While Southampton hope to conclude a deal for the versatile FC Twente defender Cuco Martina in the next few days, the situation with Alderweireld remains complicated and, potentially, fractious. The Belgium defender spent last season on loan at St Mary’s from Atlético, a deal that had been struck with a view to a permanent £6.8m move. The Spanish club could cancel the buyout clause written into the deal by paying a fee of £1.5m to Saints, but the deadline for the payment was missed.

Tottenham Hotspur have subsequently moved for Alderweireld, offering the player a five-year contract while indicating a willingness to pay Atlético nearer £11.5m for his services. Yet, according to the original agreement between Southampton and the Spanish club, Spurs are technically not yet entitled to speak with the player or put him through a medical.

The Saints’ executive director, Les Reed, has travelled to Spain to speak directly with Atlético and the club are prepared to lodge a formal complaint with the Football Association and Fifa should Spurs be permitted to sign the player.

Alderweireld had informed Southampton of his desire to return permanently to St Mary’s at the end of last season, though his head appears to have been turned since by Tottenham’s pursuit. “Of course there will be interest in the player,” said Koeman. “He is a good, strong defender and he had a good season with us. But we had a contract and Atletico were too late in paying back the option. It’s difficult. Maybe, at a certain moment, you say ‘yes’ but then, afterwards, there are other offers and it’s difficult...

“But still I believe Southampton is the best place for the player. Why? Ask the player why he told me that he was very comfortable. Very happy. He was missing playing football when he was a player at Atletico Madrid. At Southampton normally he starts every game ,and he did well. His family was happy. OK, that’s all football business. But let’s wait and see what happens in the next few days.”