United had been hoping to sign a centre-back before the deadline but hope has faded in recent days.
"The net expenditure is a record as it stands but you'd think with three weeks left for European clubs to buy Premier League players, and Premier League clubs by the looks of it not having done their selling yet, it might not stay that way".
Writing in his column for the BBC, Shearer said: "Their team is definitely already good enough to challenge champions Manchester City for the title, but can Jose get the best out them, and can they play in a style that can keep their fans happy?"
"I'm not confident", Mourinho said, when asked whether there would be more players arriving before the deadline.
"I am not confident", Mourinho said.More news: Tense calm, cease-fire follows another Hamas-Israel flare-up
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Mourinho's targets for that position were primarily Leicester City's Harry Maguire, Jérôme Boateng of Bayern Munich and Toby Alderweireld of Tottenham. "They trained Monday, Tuesday, Wednesday and today, so you can imagine they are not really fit and ready".
Marcus Rashford, Phil Jones, Victor Lindelof and Romelu Lukaku made slightly early returns so could be involved on Friday, perhaps helping to boost the mood of a manager who has looked downbeat for much of the summer.
"My view is that, first of all, is hard for me to believe we finished second", he said.
"It is hard to believe that we finished second because you are capable of making people that finish second look like they were relegated, and people who win nothing, finish below us, and you make them look like serial winners".
Matt Le Tissier believes Liverpool FC will be Manchester City's biggest rivals in the Premier League title race this term.
Figures released by Deloitte's sport business group showed top-flight clubs spent an estimated £1.23billion before Thursday's pre-season deadline - down £200million from last summer's window.