Andriy Yarmolenko this week became the fifth summer signing following the additions of Jack Wilshere, Ryan Fredericks, Lukasz Fabianski and Issa Diop.
More are expected to come with West Ham set to sign centre-back Fabian Balbuena from Corinthians while talks are also ongoing with Felipe Anderson.
But players will have to be sold and Sky Sports expert Dharmesh Sheth has heard of three players that could be going out the door – Michail Antonio, Cheikhou Kuoyate and Pedro Obiang.
He told the Transfer Talk podcast: “Manuel Pellegrini looks like it’s going to be a completely new squad under him next season.
“There’s all these players coming in and as you mention there are going to be players who are moving out of the club.
“One that is a particularly interesting one because aside from his injuries he’s done very well for West Ham is Michail Antonio. It’s our understanding that the club would consider offers of upwards of £15million.
“He’s worked all summer to get fit. He’s currently with the rest of the squad at that club training camp in Switzerland
“The noises coming from Manuel Pellegrini is he’s very impressed with him. That said, we think West Ham could potentially move him on if they get a good price for him.
“There are a couple of others who could be on their way out. It’s another surprising one as the West Ham fans I speak to like this player, particularly when he was used in a midfield role, and that’s Cheikhou Kuoyate.
“We understand West Ham are prepared to listen to offers for him. I’m told the asking price is around £10million.
“Another one is Pedro Obiang. Fiorentina and Atalanta both had bids rejected for him. It seems West Ham are listening to offers.”
West Ham are midway through their most exciting transfer window for years with joint-chairman David Sullivan this week pledging to keep on spending.
“We are delighted to have secured two very exciting signings in the space of three days,” Sullivan said.
“As a board, we assured our supporters that we would be looking to bring in high-calibre players, and Jack [Wilshere] and Andriy [Yarmolenko] fit that bill perfectly.
“Both of them have played at the highest level and we look forward to seeing that quality on show on a regular basis in the Claret & Blue.
“Jack also knows the Premier League very well, and I know all our supporters will join me in welcoming them both to the London Stadium.
“They become our fourth and fifth new signings of an already busy summer, after the additions of Ryan Fredericks, Issa Diop and Lukasz Fabianski.
“We also hope to have more exciting news regarding incomings in the near future as we aim to provide Manuel with the strongest squad possible.”