Kevin Phillips is adamant West Ham have “made a mistake” by agreeing to the deeply unpopular sale of Grady Diangana to West Brom.

The former Sunderland and Baggies striker, speaking exclusively to Football Insider correspondent Dylan Childs, admitted that he was “very surprised” to hear that the 22-year-old was allowed to leave the club.

The Hammers confirmed that the winger had joined West Brom for an “undisclosed fee” but Football Insider understands that an £18million transfer package was agreed between the two sides.

This site revealed last month that Irons chiefs had made a U-turn on Diangana’s future and were open to his sale in order to raise much-needed funds this summer.

Diangana spent last season on loan at The Hawthorns and his 31 appearances in all competitions yielded an impressive eight goals and seven assists.

When asked by Football Insider if the London-club would regret allowing the former England Under-21 international to leave, Phillips said:

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“I think they have made a mistake.

“I am surprised when I heard that they had agreed to sell him to West Brom because David Moyes said that he wanted him back and they cannot have had that many games in the space of two weeks. Haller said he really enjoyed playing with him, a striker that has not really lit the Premier League up so far…

“I am very surprised that they have decided to let him go.”

The transfer angered some Hammers first team players, a number of whom took to social media to vent their frustrations.

Club captain Mark Noble tweeted: “As captain of this football club I’m gutted, angry and sad that Grady has left, great kid with a great future!”

In other West Ham news, Darren Bent has told Football Insider that Manuel Lanzini may head fire sale of “four or five” first team players.