The Black Cats splashed out £3million to land the usually prolific striker from Wigan Athletic on deadline day in January but he struggled in front of goal in the second half of last season, only netting five goals.
Grigg is now over his ankle problem that affected him last term and he is looking to hit the goal trail this season.
Grigg said: “From January onwards it was tough for a number of reasons, I never really got going but it’s been good to get a full pre-season under my belt.
“I’m a confident boy, I will back myself to the end.
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“I’ve done it before at this level, I’ve been promoted four times and scored +20 goals in four or five times so there’s no reason why I can’t do that again.
“I will be backing myself to do that again this season,” he told the club website.
Ahead of the visit of Oxford United, Grigg added: “Pre-season has been a tough four or five weeks and personally it has been the toughest out of the 10 or 11 I’ve done.
“For this season to come around it’s exciting and I’m really looking forward to it.
“Oxford on Saturday is a brilliant game for us.
“The boys are raring to go and everyone just wants to see the Stadium of Light packed out, rocking and we’ll be making sure we put on a good performance to get everyone bouncing.”