The midfielder, who had a shocking injury record at St James' Park, was making his third start for The Hammers since joining from Newcastle earlier this month.
He was stretchered off in the 13th minute at the Memorial Stadium.
Sorry Hammers ... But We Told You So!
Dyer crumbled to the ground following, what looked like, a rather innocent challenge with Joe Jacobson on the right wing and immediately looked in severe pain.
Alan Curbishley, however, saw it in a different light and blamed the Rovers player for the injury.
Alan Curbishley, however, saw it in a different light and blamed the Rovers player for the injury.
The England international has been taken to hospital for scans but West Ham fear he has broken both bones in his lower leg.
Only this week Dyer revealed he was excited and relieved to finally become a West Ham player. And of course he said it gave him the chance to see more of his family, and he will certainly be doing a lot of that.
Dyer's transfer to Upton Park looked to have fallen through at the start of the month when Newcastle changed their valuation of the player at the last minute.
Dyer: "I thought it was the end of the move and I was devastated, but thankfully the clubs have come to an agreement and I am finally a West Ham player.
"It was well documented I wanted to be nearer to my family - but I also see West Ham as a club that is really going places.
"They have shown great ambition with the other players they have brought in and I just love the hunger of the club to be successful."