Man Utd transfer news: Alexis Sanchez has been a 'waste of money', says Duncan Castles (Image: Getty)
Sanchez, 30, celebrated a year at Manchester United this week but, in truth, there has been little to shout about.
The Chilean superstar has scored just three goals in 23 Premier League games for the Red Devils and is now way behind Marcus Rashford and Romelu Lukaku in the pecking order.
Sanchez is the top earner in the club's history - and on the highest wages in the league - but Castles has branded him a 'waste of money'.
And while Sanchez' team-mate Fred may have cost £52million, Castles thinks the same can't be said for him - yet.
"I think you have to be careful with all these new signings when you’re making judgements six or 12 months in, especially when they’re moving to a new league," he told the Transfer Window podcast.
"The history of most players who come to the Premier League, particularly top players, is one of needing an adaptation period and I think that’s especially relevant in the midfield.
"So I’d hold on a final decision on Fred. The likes of Sanchez I don’t think we need to hold onto that one because he was long adapted to the league and it’s essentially been a huge waste of money on Manchester United’s part.
"It's a big problem for them to solve and an interesting one for Ole Gunnar Solskjaer’s positivity and different managerial style, whether he can draw the pleasure in the game back to Alexis Sanchez."
Man Utd transfer news: Alexis Sanchez has scored just four goals in 32 appearances for United (Image: Getty)
Man Utd: Alexis Sanchez has head in hands at Unicef gala dinner
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Sanchez has made just two appearances under United's new interim manager due to hamstring problems.
Solskjaer insists the player is remaining positive and said: "He is a player who loves to play football and he's been hindered by injury.
"I know how frustrating that can be and how eager you are to get back. 'He's champing at the bit and his attitude has been fantastic in training. He wants to play. I'm looking forward to seeing him, and I've got loads of good players to choose from.
"I used to be one of four strikers when we played with two. Now we have six forwards and we play with three most of the time.
"There are the three who play the most but then you've got Rom, you've got Juan and you've got Alexis, so I've got a front six I can rotate. 'It's about taking the chances when you get them."