Gayle became the first player since Alan Shearer to reach the goalscoring milestone when he scored in Saturday’s 2-1 win over Brentford.
The striker limped off the field at Griffin Park with a hamstring problem.
And Gayle, signed from Crystal Palace last summer, is expected to miss several games.
The 26-year-old – who had a spell out last season with a hamstring problem – will be assessed this week by the club’s medical staff
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Gayle, however, was just happy to see United win and return to the top of the Championship thanks to a goal from Daryl Murphy, who came off the bench to replace him.
Reflecting on his 20-goal achievement, Gayle said: “It’s obviously a fantastic achievement for me.
“As I’ve said in many other interviews, it’s a credit to the team and what they’re providing for me as a lot of my goals come from inside the box.
“We’ve got great quality in the starting XI and from the boys that are coming off the bench. I’m just relishing playing with the quality I’ve got behind me.”
On becoming the first player since Shearer to hit 20 goals for United, Gayle added: “He did it every year, to be honest. So, for me, it’s the beginning and I can continue it in future.”
Murphy – who found his opportunities in the first half of the season limited by injuries and the form of Gayle – is now set for a run in the team with Aleksandar Mitrovic also sidelined.
“He’s a great player,” said Gayle. “In the past few years in the Championship, he’s been fantastic.
“He’ll bring something different. He brings great experience and will help the younger boys out. He’ll do fantastically well.”
Gayle is hopeful that he won’t be sidelined for a significant period.
Asked about the injury, he said: “It was a hamstring. I had it last season as well.
“Fingers crossed it’s not too bad, but we won’t know the full extent of it for a few days. We’ll see how it goes.”
“Obviously, it was frustrating to come off, but the three points was the most important thing.”