Andy Carroll will undergo a scan on his hamstring injury on Thursday with West Ham boss Slaven Bilic insisting "there is no reason to be negative".
Carroll lasted just 15 minutes of Tuesday's 3-1 win at Bournemouth after suffering a setback in yet another injury-plagued season.
The England striker has rarely had a consistent run in the first team since joining the Hammers from Liverpool in 2012 but did return over the Christmas period with goals against his previous employers and Southampton.
Bilic, whose side visit Newcastle United at the weekend, said at Thursday's news conference: "Andy has a scan today so we will wait for that. It's his hamstring, it's something in between a big and little one.
"Of course we will be cautious, and it is a blow for us because he was looking really sharp. He'll be back soon and he won't lose much.
"If everything goes well he will be back very soon so there is no reason to be negative."
There was better news elsewhere on the injury front for Bilic with Victor Moses, Cheikhou Kouyate and Mauro Zarate all likely to be fit for the trip to St James' Park.
"Victor Moses started to train with the team the day before Bournemouth, so he's available," added the former Croatia boss.
"Cheikhou Kouyate missed the game against Bournemouth, he was at about 85 per cent so we rested him a little bit.
"Zarate also, he felt a bit before the Bournemouth game, but it was just kind of a cramp so he's training today."
Newcastle capitalised on some poor Manchester United finishing to claim a point in a 3-3 draw on Tuesday and Bilic is expecting a tough game despite the Magpies slipping to second from bottom in the Premier League following Sunderland's win at Swansea.
He said: "We want to continue the [nine-game] unbeaten run. We're playing well.
"We are thinking only about the game on Saturday and if we get a result then the bar is going to stay where it is or even go higher.
"Newcastle had a slow start, it is a new team with a new manager. A massive club which in recent times has had difficult seasons but they are improving. They have quality, they are very dangerous and made a great comeback against Manchester United.
"I am expecting a good and difficult game in a great stadium. We're really looking forward to it."