Sunderland need to strengthen in January - Martin O'Neill

Sunderland manager Martin O'Neill says he must strengthen his squad in the January transfer window as the Premier League relegation battle intensifies.

A 3-1 loss to Manchester United at Old Trafford leaves Sunderland in 16th place, a point above the bottom three.

"We have to be seriously looking to strengthen our side," O'Neill said.

"You only have to look at the back of the programme to see we don't have any great numerical strength, never mind anything else."

Goals from Robin van Persie, Tom Cleverley and Wayne Rooney gave Manchester United a commanding lead, with Fraizer Campbell's response doing little to disguise the Black Cats' shortcomings.

"We have got a few injuries to people, but you are going to get injuries and suspensions during the course of the season and it is up to us to cope with them," added O'Neill. "That is inevitable but we just don't have that strength in depth."

O'Neill retains the support of Sunderland owner Ellis Short and is likely to be backed to bring in a centre-back, as well as more attacking options in January.

That may be all the more important given an injury to Steven Fletcher, who limped off at half-time having twisted his back in the warm-up at Old Trafford.

The Scotland striker could miss next weekend's game against Southampton.

"Steven [Fletcher] hurt himself in the warm-up, twisting his back," O'Neill said. "It was causing him a few problems in the 10 minutes before half-time and he couldn't continue."

When asked how long he might be without the player who has scored the vast majority of Sunderland's goals this season, O'Neill added: "I really don't know at the moment but it is a different injury to the one he has had in the last couple of weeks."

It was not all doom and gloom for the Black Cats and, despite three of their next four matches coming against Manchester City, Tottenham Hotspur and Liverpool, O'Neill believes he saw enough character in the final 20 minutes to remain optimistic.

"I was very encouraged by the second-half performance," he said.

"Manchester United didn't really need a helping hand from us, which they got in the first half. The goals we conceded, from our view point, were not too clever.

"That said I thought we showed an awful lot of spirit in the second half to come back into the game again. United had some decent chances to kill us off but at 3-1 we were still in the game and we had some decent chances ourselves. We could have made the last 10 or 15 minutes more interesting."