Jermain Defoe could miss the rest of the pre-season programme with a thigh injury - but medics are confident he will be back for the start of the season.
The 33-year-old hasn't featured in the two pre-season friendly games in France after picking up the injury in training.
Defoe will be sent for a scan over the course of the next few days to determine the extent of the injury, with first team coach Robbie Stockdale confirming the club won't take any risks with him.
Last season's top goalscorer - who will be given a tailored training programme - is, though, expected to be fit for the opening Premier League game at Manchester City on August 13.
Stockdale said: "Jermain picked up a little thigh strain in one of the sessions.
"You would do very well to get through pre-season without these little niggles so hopefully – once he’s had a scan – we will be able to make an assessment.
"It won’t be a long injury and I’m sure Jermain will be keen to be fit for the first game of the season, and we are as well.
"At the moment it’s probably too early to say and we don’t think it’s anything serious, but obviously with a player like Jermain you don’t to take any risks.
"I’ve been on record before and said that Jermain is a fantastic professional who works hard at his game and his fitness, so there are no issues with that and we will work to replicate some of the stuff he can do so he will be out here working and he won’t have his feet up.
"It’s not a problem, we will deal with it and move on."
Defoe watched from a bench as Sunderland maintained their 100 per cent pre-season record with a 3-2 win over Dijon FCO.
He sat alongside John O'Shea and Seb Larsson, who are yet to feature after their extended post-Euro 2016 break.
There was another injury concern for new manager David Moyes, Patrick van Aanholt limped off in the second half and headed straight down the tunnel.
Stockdale added: "At the break Patrick felt some groin tightness but he said he’d have a go and see if it would loosen off.
"There is absolutely no major issues there; whether we risk him on Saturday will depend on how he settles down over the next couple of days, but he will be fit for Borussia Dortmund."
Sunderland play their final game of their tour against Montpellier HSC on Saturday.