The striker on loan from Stoke suffered two cracked ribs in the act of scoring the equaliser in last Saturday's 1-1 draw with Doncaster, the Telegraph can reveal.

It also emerges today that Blackwell is close to landing Birmingham's former Coventry forward Gary McSheffrey amid his latest sweep for reinforcements.

But the search is widening with midfielder Nick Montgomery also heading for a lengthy lay-off. And the Blades boss is hampered by restrictions on his ever-increasing set of loan players.

United are also paying a high price for Cresswell's brave diving header on his first start for the club. "Richard smashed into the post when he scored that goal and has cracked his ribs," said Blackwell last night.

"He's now a massive doubt for our next game at Scunthorpe."

The latest blow has struck just as Blackwell was preparing to ensure a full complement of four strikers by tieing up a deal for McSheffrey. That is now not the only recruitment business on his crowded agenda ahead of two successive away games after the international break, including a trip to Blackpool.

I understand McSheffrey wants to come to Bramall Lane and that a loan pending a possible full transfer is being discussed.

The fee would be substantial albeit significantly less than the £4m McSheffrey cost when he joined Birmingham from Coventry three years ago.

The nippy 27-year-old, who can play wide or as a central frontman, has managed just 20 goals from limited appearances at Birmingham whose promotion to the Premiership has restricted his chances.

However, he had an impressive record at Coventry, boasting 53 goals from 123 starts. Blackwell sees McSheffrey as the perfect cover - and competitor - for the injured Jamie Ward. Cresswell was brought in to joust with Darius Henderson and Ched Evans, though he filled a gap wide on the left last week.

Another big hole has now opened up in midfield where United were already lacking summer signing Lee Williamson. Fellow recruit James Harper has a knee problem while Montgomery, who keeps re-establishing himself as an important presence, could be out until Christmas with ligament damage.

It all leaves Blackwell wrestling with diminishing options that may now revert to signing out-of-contract players who are searching for clubs so that he does not overstretch his loan allocation.

"The problem is that I've got six on loan and can only use five," he said. "I may have to start leaving people out because I can't play them all. It's just unfortunate. Every club has a spell like this occasionally and we'll just have to battle through."

Sixth place against the context of upheaval on this scale, not forgetting the enormous turnover of players last summer, is a creditable achievement.