After failing to make a notable impression at Newcastle United during 2017-18, Merino was sold to the Spanish outfit for a fee of £10.7m.
That has since proven to be value for money as Merino has gone on to make 233 appearances in all competitions and the majority coming from the starting lineup.
A total of 25 goals and 30 assists have been contributed, subsequently leading to 19 caps being earned with Spain, but Real Sociedad face a battle to retain his services in the long term.
There are now under 16 months remaining on his contract, something that has naturally not gone unnoticed by European football's top clubs.
At a time when Sociedad sit 10 points adrift of fifth place in the La Liga standings, they are currently struggling to convince the 27-year-old to remain at the Reale Arena.
According to Deportes COPE Gipuzkoa, Merino's representatives are not prepared to enter further discussions until it is determined whether Real Sociedad will be competing in next season's Champions League.
The assumption is that Merino will entertain offers from teams who are participating in that competition should his current side not improve during the latter stages of the campaign.
Man City and Man United are said to be closely monitoring the development of Merino, who can claim to be one of Real Sociedad's best players this term.
With regards to Man City, they are already well stocked for central midfielders and much may depend on whether the likes of Mateo Kovacic and Bernardo Silva remain at the Etihad Stadium past the end of this season.
Meanwhile, Man United are looking for stronger options in
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