It was incredibly frustrating January transfer window for Sunderland.

They did manage to complete the permanent signings of Pierre Ekwah from West Ham United, Isaac Lihadji from Lille and Joe Anderson from Everton, while they also won the race for Leeds United's Joe Gelhardt, recruiting him on loan until the end of the season.

But the failure to sign another striker is a concern for the Black Cats and it could prove costly to their play-off hopes, with Gelhardt currently the only fit striker on the club's books following Ross Stewart's season-ending injury.

Tony Mowbray had hoped to bring back Ellis Simms from Everton after his successful loan spell at the Stadium of Light in the first half of the campaign, but new Toffees boss Sean Dyche was unwilling to allow Simms to depart.

It would be incredibly difficult for Mowbray to find someone to replace Stewart's goals, but there is no doubt that further depth is needed.

With the window now closed, here are two free agents that the Black Cats could consider.

Chris Martin

Martin is available following his release by Bristol City last month.

It was a frustrating end to Martin's time at Ashton Gate as he struggled for minutes, with the emergence of the likes of Tommy Conway and Sam Bell pushing him down Nigel Pearson's pecking order.

But Martin has proven he is still a more than capable striker at Championship level, as demonstrated by the 12 goals he scored for the Robins last season, while he has had plenty of prolific seasons in the second tier previously.

There may be some concerns over the fact he is now 34 years old, but with Gelhardt likely to be Mowbray's first-choice option, Martin would be an excellent option to have in the squad.

With creative players such as Patrick Roberts, Amad Diallo, Alex Pritchard and Jack Clarke providing him with the service, you would not bet against Martin rediscovering his form from last campaign should he make the move to Wearside.

Connor Wickham

Wickham departed League One side Forest Green Rovers in January following the expiry of his short-term deal.

But it was a successful stint for Wickham at The Bolt New Lawn, scoring nine goals in 20 appearances for the third tier strugglers and perhaps most importantly, staying fit throughout his time in Gloucestershire.

The 29-year-old has been plagued by injury problems throughout his career which has meant he has so far failed to deliver on his potential, but he does have a decent track record in front of goal.

Wickham spent four years with Sunderland between 2011 and 2015, scoring 15 goals in 91 appearances for the Black Cats, including playing a crucial role in the club's Premier League survival in 2014.

There may be no better place for Wickham to settle down and rebuild his career than at a club he already has an affinity with, while he could also provide the answer to their goalscoring problems, so this is a move which could be beneficial for both parties.