A painful groin injury reduced David Nalbandian to tears as he battled past Adrian Ungur to give Argentina the lead in their Davis Cup World Group first round tie against Romania.

The world No.19 won 6-3 6-2 5-7 6-4 to hand Argentina the first point but said afterwards he may not be fit enough to play any further part in the tie, Reuters reports.

"It was one of the worst feelings I've had on a court, it's difficult to explain it to someone who isn't experiencing it," Nalbandian said in a news conference after beating the world number 183 on the clay court at Parque Roca.

"If it had been any (other) tournament in the world I'd have gone (retired hurt). At each changeover, I was crying with the pain. That had never before happened to me. It was very tough (carrying on) without being able to retire. Playing the Davis Cup at home, I'd never quit, say 'no more, I can't run any more'," the 29-year-old former world number three said. "If today I felt like this, how will I feel for five sets (against Romania's number one Victor Hanescu on Sunday)? There has to be a doubt (about playing)."

Nalbandian, who also suffered lower leg pain, paced himself through the first two sets but ran into trouble in the third, flinging his racket down when Ungur converted his set point.

Despite playing at half capacity, Nalbandian made Ungur do most of the running in the fourth set with some trademark drives to the corners and a break of serve in the third game sent him on his way to victory.