The 22-year-old was in excellent form for Athletic during the 2024-25 campaign, scoring eight goals and registering 19 assists in 37 appearances in all competitions, before playing a leading role in Spain triumphing at the European Championship.
Williams was widely expected to join Barcelona during the summer market, with the Catalan outfit thought to have activated the €55m (£47m) release clause in his deal, but the Spaniard decided to remain with Athletic.
The forward is playing in the Europa League for the Lions this season, and according to his brother and teammate Inaki Williams, he "does not regret" rejecting Barcelona over the summer.
There is again expected to be speculation surrounding Williams' future next summer, though, with a number of clubs thought to be keeping a close eye on the situation.
Man United 'enter the race' for Williams
According to Fichajes, there is firm interest from Man United, with the Red Devils identifying him as the ideal signing during next summer's transfer window.
The report claims that the 20-time English champions are prepared to make a 'considerable financial effort' in order to win the race for his signature.
Barcelona are expected to reignite their interest next year, while Arsenal and Liverpool were among the other teams to be linked with his services during the recent market.
Williams has made a slow start to this season, only managing one goal in seven appearances, but he has shown his class over the last 12 months, and it will seemingly not be too long until the Spaniard makes the move to a major European club.
Could Williams replace Rashford at Man United?
There have undoubtedly been some positives for Marcus Rashford at Man United this season, with the academy product scoring twice and registering one assist in eight appearances in all competitions.
However, he still looks some way off the player that enjoyed a remarkable 2022-23 campaign for the club and then signed a new long-term contract.
If the Englishman again struggles this season, then it would be best for both parties to move on next summer, which would put Man United in the market for a new left-sided attacker.
Rashford has only managed one Premier League goal this season, with his best performance of the campaign coming against Barnsley in the last round of the EFL Cup.
The forward is currently preparing for Sunday's Premier League clash against Tottenham Hotspur, and he has managed six goals in 16 senior appearances versus the North London outfit.