Blackwell paid an estimated £1.5 million to secure the former Wigan winger's services this summer following a series of sparkling displays for the club on loan but has failed to select Cotterill for either of United's last two games.

But the United manager, who planned to reveal whether a clutch of trialists, including Kiki Musampa and Seb Carole, will be offered permanent contracts before Bristol City's visit to Bramall Lane today, said: "Everyone needs a shot across the bows from time to time.

"If you don't get that then people will go past you.

"We know how good Cotts can be and he's had a wake-up call but I'm sure he'll respond.

"I had a little chat with him before the Watford match and told him why I was leaving him out.

"I always do that to players: , explain why they're being left-out, so they know what aspects they have to work on in training.

"I'd never just do it and say nothing.
"I want Cotts to get back to doing what he does best - attacking players and getting crosses in - and, to be fair, he's reacted brilliantly."

Having already signed Barnsley's Brian Howard and Southampton's Nathan Dyer on loan during the emergency transfer window, Blackwell hopes to add at least one more new face to his squad before the derby with Sheffield Wednesday later this month.

Musampa, previously of Manchester City, joined United for training on Monday but Blackwell has also received enquiries about several of his own players with Keith Gillespie known to be interesting Burnley.
"I've had a couple of calls," Blackwell added.

"Regarding Kiki, I'll sit down with Sam (Ellis, Blackwell's assistant) and have a chat because he's been doing a lot of work with him.
"Then hopefully we'll come to a decision.

"I always give people at least a week because it can be hard to set the world alight during their first few days."

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