West Ham United were beaten 2-0 by Watford in David Moyes’ first match in charge.
Bilic was let go by West Ham at the start of the month, after what had been a disastrous start to the campaign.
The Hammers have since appointed David Moyes, but the Scottish boss was unable to guide the Hammers to victory during his first game in charge.
West Ham were beaten 2-0 by Watford at Vicarage Road on Sunday, and Obiang has blamed the display on the players’ poor fitness levels.
He said: “We need time to understand better what he wants and we have to work a little bit more to be fit to do the things he wants.
“I’m agreeing with him because he is angry we lost the game. He thinks we can do something better and we have to do more.
“We have to work hard for the next game.”
Bilic faced criticism from West Ham fans for being too laissez-faire with his approach to training, and Obiang’s comments hardly reflect well on the Croatian boss.
Moyes has demanded that West Ham show more effort and energy under his stewardship than they did under Bilic already.
West Ham are currently in 18th place in the Premier League table, with the pressure rising at the London Stadium.
Moyes takes charge of his next West Ham match on Friday, when his side take on Leicester City.
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