Cardiff City manager Ole Gunnar Solskjaer was disappointed with the condition of "two or three" players as they began pre-season training.
The Bluebirds returned on Thursday, 3 July with Solskjaer happy with most players' levels of fitness.
But he added: "I'm not going to play players who're not fit enough for this league because you've got to be fit to play in the Championship.
"There's two or three exceptions who have to do some extra."
The former Manchester United striker did not name the players, but added he expected everyone to meet the same standards.
"They know that's disappointing, but it's up to them to catch up with the rest of them," said the Norwegian.
Cardiff were relegated in May after one season in the Premier League and start their Championship campaign at Blackburn Rovers on Friday, 8 August.
The players have their first pre-season run out on Monday, 7 June when they face Welsh Premier League side Carmarthen Town in a friendly at Bridge Meadow Stadium.
Solskjaer confirmed Cardiff have accepted a bid from Queens Park Rangers for England international defender Caulker and that clubs had made inquiries about Chile international Medel.
Both players are reported to have release clauses in their contracts which were triggered when Cardiff were relegated while striker Campbell has been linked with Crystal Palace and Leicester City.
Solskjaer did not rule out players leaving, but did not anticipate much business "coming in".
"Some players will be sold because I cannot hold a squad of around 30 outfield players - that's not possible," added Solskjaer.
"Of course if you lose too many you'll have to replace them, but I've already done a lot of business."