Injuries to Billy Jones and Didier Ndong disrupted Sunderland's gameplan admits Robbie Stockdale, with the seriousness of the injuries to be assessed.
Jones endured a Tees-Wear derby to forget after failing to prevent Marcus Tavernier from giving Middlesbrough the lead at the near post six minutes in.
The right-back was then booked before injuring himself in a collision with teammate Darron Gibson, Jones subbed after less than half an hour.
Ndong, arguably Sunderland's best player, was forced off after just 55 minutes with an injury to his right knee after sliding on the turf.
It forced joint caretaker boss Stockdale into two forced substitutions with concerns throughout over John O'Shea's calf too.
It meant Paddy McNair, who was starting his first game in 11-months following a serious knee injury, had to play longer than originally planned - the Northern Ireland international subbed after 77 minutes.
Duncan Watmore wasn't involved at all but it is not thought to be serious while Lamine Kone was ruled out and will be assessed.
"We were forced into substitutions early and Paddy played longer than we were hoping he would play," said Stockdale.
"That injury to Billy and then to Didier probably affected our game plan a little bit and then John O'Shea was struggling with his calf a little bit, so we were holding on for the next substitution as it would have been our last one.
"We lost Duncan with a little niggle on Friday and Lamine the day before.
"I thought the effort and the attitude of the players was first class but we didn't create enough second half to put Middlesbrough under pressure.
"The fans turned out again in their numbers, we wanted to put on a performance and get a result but we didn't quite do that."
On Ndong's injury, Stockdale said: "No it is too early.
"He is getting assessed, I would imagine with all the players, Billy, Duncan and Lamine we will know in the next few days."
O'Shea's calf niggle won't prevent him joining up with the Republic of Ireland squad during the international break.
Stockdale added: "It was very slight.
"John just felt a twinge in his calf, it was just something in a game that affects the substitutions.
"It is not ideal to use two substitutions for injuries within an hour."