Ole Gunnar Solskjaer was heard shouting "Start moving" and "Some movement" at Anthony Martial before taking him off against Newcastle.
The Manchester United forward was leading the line on Sunday night, but was ineffective in what was a drab first half at Old Trafford.
Solskjaer made it clear to Martial he wanted to see more from him in the second half but the Frenchman failed to improve his performance after the break.
Solskjaer made one last attempt to spur the striker on, shouting at him to "start moving".
But eventually the Red Devils boss opted to hook Martial, replacing him with young England international Mason Greenwood.
United, who were 2-1 up at the time of the substitute, thanks to goals from Marcus Rashford and Daniel James, netted once more from the spot via Bruno Fernandes.
The win sees United reclaim second place and keep pace with champions elect Man City.
Solskjaer said of the match: "We had to find a way to win it in the second-half. The first-half wasn't up to the standard that we wanted.
"Maybe because of Newcastle, maybe because of what we did in the week. We asked them to go again after a high-intensity game and it took us to half time to get our legs and energy."
Newcastle boss Steve Bruce added: "Fulham have had a good week and won a couple of games, which at the bottom end of the table is big, but there are a few of us: Brighton, Burnley and maybe Crystal Palace looking over their shoulders.
"My message to the supporters is that I'm convinced we'll be OK."
