Sheffield United face a crucially important summer transfer window.

If the Blades can strengthen their side sufficiently and add quality options to pad out their squad, then they are capable of building on last year's success and mounting a serious promotion bid.

But this could easily be derailed if they fail to bring in the right players this summer.

Chris Wilder has built a strong squad at Bramall Lane but he needs to add strength in depth to give himself more options.

There are too many members of his current squad that are not quite at the level required to compete for promotion to the Premier League and they need flogging this summer and replacing with better ones.

Wilder will have drawn up a long list of potential transfer targets and here are six players that would slot seamlessly into his Sheffield United squad.

Blackman was one of Sheffield United's best players last season during a loan spell from Chelsea.

The 24-year-old is keen on a permanent return and this move suits all parties.

The Blades have been looking for a dominant, young centre-half for a while now and Clarke fits the bill after establishing himself as one of the best defenders in League One.

Just as they did with Enda Stevens last year, Sheffield United should poach the 21-year-old from Portsmouth after he won the club's Player of the Year accolade.

Wilder needs to add at least one new full-back to his current options to give him depth in that department.

Ward can play on either side, as a centre-half or in defensive midfield, making him the perfect addition on a free transfer.

To add a creative spark in central midfield, Oztumer would be an excellent acquisition on a free transfer.

After scoring 17 goals last season and grabbing a number of assists, the 26-year-old - dubbed the "Turkish Messi" - would improve Wilder's options.

Another creative midfielder to consider is Peterborough United's Maddison - who has been transfer listed to further his career.

The 24-year-old consistently hits high figures in both goals and assists at League One level and his tally of 10 goals and 21 assists last season indicate that he is ready to step up.

The Blades possibly need one more striker in their ranks to rival Billy Sharp and Leon Clarke.

McBurnie is available for a compensation fee if he leaves Swansea City and the 22-year-old's tally of nine goals in 16 starts for struggling Barnsley shows that he is already a top striker at this level.