League One latest: Portsmouth rivals Sunderland suffer another huge injury blow | Wigan issue Charlie Wyke update | Plymouth boss makes honest admission

The 27-year-old has been struggling with a shoulder injury for most of the season, suffering repeated dislocations.

He missed the Black Cats’ 2-1 win at Cambridge United on Saturday after being in consultation with a surgeon last week.

Now it has been decided that an operation is needed – a procedure that could see him out of action for up to nine months.

Sunderland boss Lee Johnson is already without the likes of Aiden McGeady, Jordan Willis, Niall Huggins, Denver Hume, Lee Burge and Dennis Cirkin – while Corry Evans has also been added to that list in the last 24 hours.

That saw the Wearsiders name just six substitutes on their bench at the Abbey Stadium, leaving Johnson to admit that the January transfer window couldn’t come quick enough.

He told the Sunderland Echo: ‘He (O’Nien) needs to have an operation.

‘He’ll be out for three months minimum, anywhere between three and nine depending on how much they have do.

‘We might have to register myself and Jamie McAllister! I’m going to have to be tactically flexible and every now and then we’re going to have a square peg in a round hole.

‘We probably had fifteen players (on Saturday).

‘We’ll have to go again in this tough spell and bundle through to January.’

Wigan moved joint top of League One with Rotherham after they secured a late 2-1 win at Plymouth’s Home Park.

However, their thoughts were still with striker Charlie Wyke, who collapsed in training at the start of last week.

He remains on hospital, where he continues to be monitored.

A club statement said the 28-year-old is in a stable condition and in communication with his family.

Yet the former Sunderland forward will not be available for selection for the immediate future.

The statement added: ‘With Charlie's approval, we can confirm that Charlie has not received a COVID-19 vaccination and Charlie's collapse was not related to any COVID-19 vaccination’.

Wigan’s win at Plymouth was the hosts’ third defeat in the space of a week.

That has seen them swap pole position in the division for fourth spot – and resulted in Pilgrims manager Ryan Lowe admitting that has side have been ‘over-achieving’ this season.

He told Plymouth Live: ‘We are not ready for top of the table, let's have it right. We are competing against big budgets and whatever else.

‘We are where we are, we are way over-achieving what we set out to do. That's just the way we are. We are not moaning about it.

‘We have had a fantastic start (to the season) and we have had a horrendous week. We have got to put that week to bed.

‘If you had said to me at the start of the season that after 20 games we would be sitting on 36 points and in the second round of the FA Cup I would have bit your hand off for it.

‘It has been a disappointing week but let's not forget we have been outstanding up until then.’