Groves earned scores of 117-112, 116-112 and 115-113 over his English rival at the Manchester Arena on Saturday, but went straight from the ring to hospital after suffering a suspected dislocated left shoulder in the last round.
Victory over Eubank in a second defense of his World Boxing Association (WBA) super-middleweight title also secured Groves a place in the final of the eight-man tournament.
“I haven’t diagnosed it yet but it feels pretty sore,” Groves said in the ring afterwards before missing the traditional post-fight press conference.
“I wasn’t going to let anything beat me. I’ve boxed on with cuts, broken jaws, everything. Here, I wasn’t going to let any injury get me out.
“It was about who wanted it most I think, and I obviously wanted it most,” added Groves, still due to fight the winner of the second semifinal between England’s Callum Smith and Germany’s Jurgen Braehmer on February 24.
The WBSS final is meant to take place at the O2 Arena in London on June 2, but Groves’s trainer Shane McGuigan said there are now concerns over whether the champion will be fit by then.
“He suffered a shoulder injury in the last round, we don’t know what that is at the moment but hopefully he can box again soon,” McGuigan told a press conference.
“After a performance like that he’s the best super-middleweight on the planet. We fulfilled the game plan to the T and executed it perfectly. We beat them on many different levels.”
“We will wait until Monday. With those sort of injuries you can train very quickly again — if it’s a case of it just popping out. No one knows until it has been scanned.”
Sauerland said that despite losing, Eubank could find himself in the WBSS final if Groves is ruled out through injury.
“He will definitely be on the list,” said Sauerland. “It’s a decision that’s taken by the (WBSS) board. I will make my recommendations.”
Eubank Jr, 28, said he was hampered by a cut above his right eye suffered in the third round.
“This is the first time I’ve been cut in my career,” he told reporters.
“I couldn’t see out of my right eye for pretty much most of the fight and that affected my style. I had to resort to loading up. Every time he moved to my right, I couldn’t see him.
“In the later rounds I was hurting him with a lot of shots. I thought I did enough in the later rounds to nick it, but George had a good game plan.”
Eubank’s father Chris Sr, who was world middleweight and super-middleweight champion in the 1990s, admitted Groves deserved the decision.
“He (Junior) didn’t perform,” said Eubank Sr. “He’s a lot better than what you saw because he was loading up. He didn’t close him down. No combinations, just power, but that’s okay, he will live and learn.
“George fought the right fight, staying off, feinting, and when he came in, he held. It was perfect tactics.”