Former Liverpool managing director Christian Purslow claims Manchester United took advantage of a "once in a generation opportunity" when they signed Alexis Sanchez from Arsenal for "not much money" in the January transfer window.

The Chilean international left the north London club and completed a switch to Old Trafford on 22 January, and as a part of the deal, the Red Devils allowed Henrikh Mkhitaryan to move in the opposite direction.

Sanchez came close to joining United's local rivals Manchester City last summer. However, Arsenal's failure to sign Thomas Lemar from AS Monaco on the deadline day of that transfer window forced them to retain the forward's services until mid-January.

Prior to the start of this calendar year, it was believed the 29-year-old will reunite with his former manager Pep Guardiola at the Etihad.

Purslow stressed that no one in the game ever saw United beating City for Sanchez's signature before the start of the mid-season window.

"I don't think they did [anyone in the game saw Sanchez joining United before January]. I think everyone thought that [Sanchez to City] was a done deal," Purslow told Sky Sports.

"We will never quite know the sequence of events that led to that potential transaction winding away into a United purchase.

"It has the look from the outside, I don't know this to be true, that Arsenal out of nowhere had their dreams come true.

"Rather than being in a unilateral discussion with City taking their best player nearly on a free, they had a little auction going when Mourinho and Antonio Conte both spoke up in early January that actually getting Sanchez was a once in a generation opportunity to buy a top player for not much money down."

Purslow added that Sanchez's deal for United was a "brilliant outcome", while also admitting that getting Armenian international Mkhitaryan as a part of the swap deal was a "pretty good outcome" for Arsenal.

"Brilliant outcome for United, pretty good outcome for Arsenal on balance, but I suspect not a very happy camp at City around the way that deal was conducted," he explained.

"I think Arsenal suddenly had a little auction going. I suspect when Sanchez's agent said to Manchester City's executive team, 'You might have to improve my deal up a bit because United are here' – that [would have] felt like a breach of trust.

"They thought they had a handshake deal at best. I bet they were very angry about that and I suspect they thought, 'Actually let's walk away from this deal,' leaving Manchester United to sweep him up."

Sanchez made his United debut against Yeovil Town in the fourth round of the FA Cup, with Jose Mourinho's side progressing further in the competition after securing a comfortable 4-0 win. His league debut for the Red Devils ended in disappointment, however, as they suffered a 2-0 defeat at the hands of Tottenham Hotspur.

Alexis Sanchez
Alexis Sanchez joined Manchester United from Arsenal in January Getty