Manchester United are pursuing Liverpool's Alexis Mac Allister in what would be the first direct transfer between the fierce rivals in more than six decades. However, one of his fellow Argentinians may be positioned to provide some valuable guidance on such a move.

Gabriel Heinze has expressed regret over his behaviour when attempting to force a switch from Old Trafford to Anfield. The former left-back was in his prime but found himself competing with Patrice Evra for a place in Sir Alex Ferguson's starting XI. Consequently, Heinze pushed for a transfer to arch-rivals Liverpool, who allegedly had a £6.8million bid turned down. The most recent player to move directly between the two adversaries was Phil Chisnall in 1964, with Ferguson being a particularly staunch defender of the unwritten rule prohibiting such deals.

That stance was likely amplified in Heinze's situation given the defender's insistence on the transfer. When addressing his circumstances at the time, though, he appeared not to fully comprehend the severity of his request.

"My fight is for the freedom to negotiate with any club," Heinze told the Daily Mail in 2007. "United never wanted me to leave for one of the big clubs, but this anti-Liverpool clause is incredible."

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However, his viewpoint evidently mellowed over time. The Argentinian even confessed to regretting his conduct and the manner in which his departure from Old Trafford unfolded.

"I don't have many regrets from my career as a footballer, but that episode with Ferguson [has] to be one of them," he admitted years later. "I'm impulsive and strong-willed, and this has got me into trouble at times, which was the case when I left United.

"I spent three years in Manchester and had some great moments and I regret [leaving the club] a lot. There are a lot of things I regret from the last months, but I am a strong personality, Sir Alex is a strong personality. I took the decision and, looking back, I regret it because it meant leaving a great club and their supporters.

"I was aware of the rivalry [with Liverpool], I knew the risk of going from Manchester to Liverpool and what it means. I hope it doesn't tarnish the way they [the supporters] see me and they will remember the three years I had in the team."

Ultimately, Heinze transferred to Real Madrid for £8m in the summer of 2007, spending two seasons in Spain before relocating to Marseille. The South American has since transitioned into management himself and currently serves as a first-team coach under Mikel Arteta at Arsenal.

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Should World Cup-winner Mac Allister take anything from Heinze's experience, it might be to avoid pursuing a transfer to Manchester. That said, such a scenario seems improbable despite Liverpool's recent struggles this campaign.

United could find themselves seeking a statement midfield acquisition if Bruno Fernandes departs Old Trafford later this year. Mac Allister, who has flourished operating centrally or in a more attacking No. 10 role, would represent an ideal solution tactically, although the practical challenges of facilitating such a deal might prove insurmountable.