Arsenal will reportedly only be able to sign Chris Smalling if Manchester United succeeds in signing Kalidou Koulibaly.
Smalling has become a target for the Gunners after turning his career around in Italy.
The 28 years old joined Roma on loan in the summer after falling down the pecking order at Old Trafford.
He has played 28 times for the Italians this season and has been in fine form. His form has attracted the attention of Premier League sides who hope to give him another chance in the division.
Arsenal is one of his main suitors at the moment and the Gunners reportedly have no problems paying the £25 million that the Red Devils want for his signature.
However, they face increasing competition from Roma and a recent report from Sun Sport claims that Manchester United will only allow him to leave if they sign Koulibaly.
The same report claims Koulibaly has told Napoli that he wants to leave them in the summer and United remains one of the teams in the running to sign him.
The Senegalese star is usually mentioned in the same bracket as Virgil van Dijk and Sergio Ramos and he is set to cost whichever team that eventually signs him up to £90 million.