Chelsea's hopes of selling Diego Costa to Atletico Madrid has hit another stumbling block over the forward's wages.

The two clubs stepped up negotiations earlier this week over a transfer which would cost an initial £41m, but with various add-ons taking the fee up to Chelsea's asking price of £50m.

However, Atletico can't register any new players until January and they are having second thoughts about paying his salary while he is not available for selection.

A loan move - Everton, Marseille, AC Milan and Monaco are all interested - would provide a solution.

But due to Costa's lack of fitness, there is a fear on Atletico's side that no club will actually want to go through with it.

The 28-year-old has been AWOL in Brazil for over six weeks and has refused Chelsea's request to return to training in London.

He has been doing individual work-out sessions, but is still a long way from being able to play first team football again.

Costa's last game was for Spain against Macedonia in June and is believed to be several weeks away from match fitness.

Atletico fear that no club will want to pick up Costa's salary if it means that he is only in the first XI for two-three months.

Given Diego Simeone's side can't name him in the squad until the new year, they are not in a rush to complete terms and could decide to wait until the next transfer window.

The deadline for Spanish clubs to complete signings is 24 hours later than for English sides - it shuts at 11pm tomorrow night UK time.

Sources in Spain suggest that Atletico don't plan to meet with Chelsea again to talk about the deal until next week.

Chelsea are wary that this could be just a late negotiating tactic by Atletico to trigger a cut price deal.

Costa is currently paid £150,000-a-week at Stamford Bridge and is so desperate to secure a move back to Atletico, he could be prepared to take a pay-cut.

The Spain international has scored 52 League goals for Chelsea since joining from Atletico for £32m in 2014.

He helped them win two titles, including the 2016-17 campaign which was Antonio Conte's first season in charge.

But the duo fell out at the start of the year amid an offer from Chinese Super League side Tianjin Quanjian's worth £570,000-a-week to the forward.

Conte insists that is when Costa was informed he would be sold in the summer, but the latter insists he was told by text message by the Italian two months ago.

His lawyer has threatened legal action, while Chelsea have been fining him during his absence in Brazil over the last six weeks.