Chelsea midfielder Gallagher has completed his medical ahead of a potential £33.7million move. However, Atletico need to sell a player before the deal can go ahead.
The collapse of the Omorodion deal raised questions about Gallagher's move, but the 24-year-old could still depart.
Chelsea have reportedly made an offer for Atletico Madrid forward Joao Felix
Chelsea's offer for Felix could total £55million (€65million).
According to O Jogo, Chelsea have offered a guaranteed initial fee of £30million (€35million) for Felix, with £25million (€30million) to be paid later for the remaining percentage of the transfer fee.
Felix is open to joining Chelsea but the two clubs have yet to agree a deal.
Chelsea turned their attention to Felix after missing out on fellow Atletico forward Omorodion.
Omorodion had been poised to sign for Chelsea for £34.5million on a seven year deal with an option for a further year. However, negotiations hit a hitch at a late stage.
Felix previously had a loan spell at Chelsea in 2023, during which he scored four times in 20 appearances.
Last season Felix found the net on ten occasions in 44 appearances while on loan at Barcelona.
Chelsea, now managed by Enzo Maresca, have been heavily active in the transfer market this summer, with their most prominent move seeing Pedro Neto arrive from Wolves for £54million.