West Ham captain Mark Noble went down injured in the second half
Noble came off after just 54 minutes with an ankle injury picked up after the restart.
And the West Ham captain is set for a scan, leaving his manager sweating.
“We have to wait to see the results of a scan,” Bilic said.
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“To lose the skipper who is a leader and a mentor in the middle, he keeps the team in shape, it was a blow.
“It’s all about the squad."
Noble came off after just 54 minutes at Middlesbrough
Slaven Bilic (right) says Nobel will have a scan
Andy Carroll scored twice for the Hammers in their win at the Riverside and the striker revealed why he came off in the second half when on a hat-trick.
"I didn’t train all week and had a couple of days off, so I didn’t want to risk anything," he said.
"I'm all good, looking forward to the next game. The lads played well and the goal at the end to kill the game was fantastic."