The Black Eyed Peas star was picked up on by viewers after seeming to forget about one of his two acts.
Will told Team Jennifer Hudson singer Jamie Miller that if his contestant Michelle John didn't win, he wanted Jamie to.
"I would be like completely, completely honest. So, if Michelle doesn't win The Voice, and you won The Voice, I wouldn't be mad at all," Will said.
He went on: "Hold on, here's the reason why. Because, it's really important.
"I mean now this is like 'why would I even say this?'. It's important that the show has a star and stuff, and I think Michelle could be a star.
"Right? She can be a star. And if she wins The Voice she will be a star, but god darn it if she doesn't win it better be because you won."
All nice words for Michelle and Jamie, of course, but some viewers weren't sure that Will's other contestant Jason Jones would have appreciated them.
"If Michelle doesn't win, you'd better' Will totally throwing Jason Jones under the bus there, eh? #thevoiceuk #thevoice," one viewer remarked on Twitter.
Another quipped: "Jason's currently backstage giving Will the finger 😂 #thevoiceuk"
It's the second week in a row that viewers of the show have turned on Will, who has been a coach on every series of The Voice UK so far.
Following last Saturday's live show, viewers slammed the rapper for his 'disrespectful' attitude to performances, spending most of the episode on his phone.
Will was also criticised for his fast pass choice in the results show after again taking FOREVER to make a decision.
"Will i am get off the phone and respect the contestants! You put through your worst person because u didn't know what 2 do! Poor girls!" one fan complained.
Another added: "#TheVoice is Will I am getting paid per minute of airtime he is on screen. Get on with it"
And a third wrote on Twitter: "Will's annoying antics have finally got too much for me, time to turn off The Voice. It's had its day! #TheVoiceUK #William #Extinguished"
The Voice UK continues Saturday nights on ITV.