Manuel Pellegrini said it was not a "good idea" for Marko Arnautovic to play for West Ham at Bournemouth amid continuing speculation over the forward's future.
Arnautovic has been linked with a move to the Chinese Super League and the Austria international's agent and brother confirmed he wants to leave West Ham.
West Ham were beaten 2-0 by Eddie Howe's Bournemouth on Saturday, with Arnautovic left out of the squad by Pellegrini.
And the West Ham boss confirmed Arnautovic was not selected because of the ongoing speculation over his future at the club.
"As a manager you must make decisions on the players that work better during the week," he told reporters.
"Marko has another issue so I thought that it was not a good idea for him to play.
"We don't need to talk about a player that was not in the squad. I never complain about players who are not here.
"We have nine players injured, let's talk about the ones here that we brought to play this game.
"We didn't win, Marko Arnautovic didn't play so we must have other players to step up."
Thank you for your support today, Claret & Blue Army pic.twitter.com/ERGQFiGyds— West Ham United (@WestHamUtd) January 19, 2019
Callum Wilson and Josh King goals condemned West Ham to their second consecutive 2-0 defeat away from home in the Premier League.
"Of course we are disappointed about the result," Pellegrini added. "It was a very close game in the first 45 minutes, and in the second half we had a clear opportunity to score the first goal.
"We didn't and then they scored a beautiful goal, but one which had a lot of luck too because the rebound came in exactly the position for their player to shoot.
"We had a reaction, but we couldn't score and if you can't score you don't win the game. We are disappointed about that because this was our opportunity to go to seventh in the table, but football is like that.
"Maybe sometimes you play games in which you deserve a better result, but you don't get it."