By Anthony Marshall - Newcastle United Managing Editor
Midfielder Colback has been sidelined by a hamstring injury for the last four weeks, while forward Riviere made his only appearance of the campaign against Watford last month before suffering a slight hamstring complaint.
However, the pair have been back in full training and are in contention for a place in the Magpies' side at Stamford Bridge.
"There's two to be added to the squad.
"On the injury front, after Chelsea we have an 18-day break before the next game.
"We hope that maybe three or four come back from injury into the squad, which will be a real boost."
During that two-and-a-half-weeks without a fixture, United will travel to La Manga, in Spain, for a warm-weather training camp where they will also take on Norwegian outfit Lillestrom in a friendly.
And McClaren has refuted any suggestions that it will be a spell of rest and relaxation for his squad.
"Definitely not," he continued. "We could have done that and gone to much warmer climes and more luxurious places.
"But this is a training camp. We believe there is a lot of work and preparation (to be done).
"We have injured players coming back who need work, and we need togetherness because from Stoke onwards it's game after game.
"It's the most critical part of the season when you're coming into the last ten (games).
"But we're in a position where we're still in that battle to climb up the league, to get out of the bottom three, and it's absolutely critical that we get some work done to prepare for the end of the season.
"We also needed a game and it was difficult to find one here. It's an ideal opportunity to arrange a game behind closed doors."