The Red Devils will be looking to splash the cash at the end of the campaign once a new manager replaces current interim boss Ralf Rangnick.
According to the Mirror, United have their eyes set on Real Sociedad forward Isak, who was linked with a move to Arsenal last week after being spotted in London.
Chelsea are also said to be keeping tabs on the 22-year-old and the La Liga side know they face a fight on their hands to keep hold of him if he continues to build on his eight goals in all competitions this term.
Isak won’t come cheap with interested parties needing to meet his £75million buyout clause in order to tempt Sociedad into doing business.
United could be tempted to fork out though as they see Isak as a potential replacement for Ronaldo, should he leave in the summer.
Chelsea will also enter the race if Romelu Lukaku’s form doesn’t improve with Timo Werner also yet to convince Thomas Tuchel.
Isak, who has won 32 caps for Sweden, remains on Arsenal’s radar but the Gunners will need to qualify for the Champions League if they are to be considered a serious option for the forward.
Last month, United legend Rio Ferdinand backed Isak as an ideal signing for the north London side.
‘He will be a good signing,’ he said.
‘Another young talented player. He has done really well in the Euros for Sweden, I thought.
‘He is a talented player, man.’
But United will be keeping a close eye on Isak in the coming months given they could find themselves in desperate need of a striker come the summer.
Anthony Martial completed a six-month loan to Sevilla last month and looks unlikely to have a future at Old Trafford upon returning, while Edinson Cavani needed to be convinced to stay in January as he looked for a way out.
Ronaldo is under contract until the summer of 2023 but speculation continues to not go away of links with PSG with his return to United not quite going to plan given their poor season so far.
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