SIMON GRAYSON is pressing ahead with making further changes to Sunderland’s squad ahead of this week’s Championship opener, but Lamine Kone could still have a future under him at the Stadium of Light.

Kone infuriated supporters on Saturday when he turned in a poor display during the woeful 5-0 defeat to Celtic on Wearside, even if he was not the only one to disappoint on an afternoon to forget.

The Ivorian defender has frustrated fans during the last 12 months because he has rarely reproduced the standards which attracted Everton offers in the region of £20m last summer.

Burnley and West Brom are two of the clubs seriously interested in signing him before the transfer window closes at the end of next month, although Sunderland will not get anywhere near that sort of figure now.

The likelihood is the African centre-back will be moved on, and that has led to suggestions from fans that the manner of his recent displays are because he has eyes on leaving.

But Grayson has defended Kone, who was replaced just after half-time against Celtic having played almost all of the previous two matches against Scunthorpe and Bradford.

“Lamine was not in the best physical condition. He was feeling fatigued,” said Grayson. “Fair play to him because he played 85 minutes on Wednesday and 90 minutes before that, so maybe Celtic was a game too far. He was one of a few that struggled so you can’t blame Lamine for the result.”

As well as addressing Kone’s future, Grayson knows he is still short of where he wants his squad to be to attack the new season after seeing Celtic embarrass his Sunderland team in the final warm-up friendly.

He is still in the market for more players, including goalkeeper Robbin Ruiter. The free agent is also interesting Burnley after impressing during his two matches on trial with the Black Cats.

Grayson, who revealed Wahbi Khazri will be monitored after sustaining a knock against Celtic, said: “He (Ruiter) was always going back to Holland. Hopefully we will be able to conclude the deal.”

Sunderland have rejected an offer from Besiktas for Jeremain Lens. The Dutch forward has shone during his pre-season outings and would be a huge asset, although the money raised would allow Grayson to tinker further.

Lens was missing against Celtic and he could yet have played his last game for the club if another bid is received before Friday’s season opener with Derby County.

When Grayson named his side to face Celtic the line-up did look as strong as it could be and there was every chance it would be that which started against Derby. Having shipped five without reply, though, the former Preston boss may well have had a rethink.

“After this it’s not my (starting) 11!” he joked. “I said all along that this was not a rehearsal for Friday. They can play themselves in and out of the team. We will sit down and go through what we need to do better.

“This has come along and it is a big week for us in terms of preparation. There are a lot of things that have gone wrong that we need to put right.

“The opposition was decent but it’s about stopping the opposition from playing. They are decent players here otherwise they wouldn’t be at this football club but you need work and have desire too. You need to do whatever it takes to make sure you don’t concede.”

Sunderland have had a mixed bag of results during pre-season, but the manner of the defeat to Celtic raised even greater concerns than those which surfaced during the St Johnstone reversal.

A highlight of how Grayson felt was how he ordered the players in from a post-match warm down after just one run so all of his players could hear what he had to say.

Sunderland were a goal down inside five minutes when new signing Jason Steele’s poor pass was not dealt with effectively by Kone and Callum McGregor capitalised.

McGregor added a second soon after when he slid a finish beyond Steele after a free-flowing move which cut open the Sunderland defence and ended with Scott Sinclair’s defining pass to his team-mate.

The third arrived with six minutes remaining of the first half. Steele parried away Olivier Ntcham’s curling effort towards the far post and it fell invitingly to Jonny Hayes. The former Aberdeen winger, who was not closed down quickly enough by Brendan Galloway, picked out the far corner with the rebound.

The frustrations grew when Aiden McGeady hauled down Tony Ralston in the box. McGregor - showing James Vaughan how it should be done after his second penalty miss for the club - completed his hat-trick nine minutes after the break from the spot.

Steele was beaten again with 23 minutes remaining. Stuart Armstrong found himself in space 20 yards out so he tried his luck, dispatching a low shot that was hardly flying in and it found a way through a crowded box and inside Steele’s far corner.

Grayson, who suggested Vaughan will have the penalties taken off him, said: “It’s an eye opener for everyone. Just when you think you are going along in decent fashion it is obviously disappointing to suffer a result like that.

“We didn’t work hard enough, there were too many errors, too many bad decisions and when your decision making is like that against a strong team like Celtic they will punish you.

“You can’t make decisions like that at any level of football. It was a wake-up call. What could go wrong did go wrong. We have had a really bad day and we start to put that right.”

SUNDERLAND (4-2-3-1): Steele; Jones (Matthews 75), Browning, Kone (O’Shea 53), Galloway; Cattermole (Gibson 75), Ndong; Grabban (Asoro 66), Khazri (Honeyman 31), McGeady; Vaughan. Subs (not used): Djilobodji, Love, Embleton, Mika (gk), Stryjek (gk).

CELTIC (4-2-3-1): de Vries; Ralston, Ajer (Benyu 70), Tierney (Hill 64), Miller (McCart 70); Kouassi (Aitchison 81), Ntcham (Bitton 46); Hayes (Rogic 46), McGregor (Henderson 73), Sinclair (Armstrong 46); Forrest (Ciftci 64). Subs (not used): Hazard (gk).