Ronaldo celebrated his 37th birthday on Saturday and is tied down to the Red Devils until 2023, but there have been suggestions that the attacker could leave earlier than planned owing to Man United's underwhelming season.
Ralf Rangnick's side do have the option to activate a 12-month extension for Ronaldo, but United are still understandably starting to plan for life without the five-time Ballon d'Or winner.
According to The Mirror, Man United are already making plans for Ronaldo's possible summer departure by plotting a swoop for in-demand Sociedad forward Isak.
The Sweden international fuelled speculation surrounding a deadline day move to Arsenal after being pictured in London, but he remained in La Liga after the window closed.
The report adds that a lack of Champions League football could hinder the Gunners' chances of landing Isak, who is also rumoured to be attracting glances from Chelsea.
The 22-year-old has only registered four goals in 18 La Liga appearances this season and is reported to possess a £75m release clause in his Sociedad deal, which does not expire until 2026. body check tags ::