Gabbidon was stretchered off the field in the 64th minute of the game against Sheffield United after a challenge from Sheffield's Christian Nade.
The influential Welshman went for a scan on Sunday and Head physiotherapist Steve Allen revealed the bad news.
“Danny has suffered a grade two tear to his lateral hamstring muscle and the estimated recovery time before he is back playing again is around four weeks.
“We are hopeful that he may be back sooner than that but his recovery won't be rushed.
“We arranged the scan for yesterday so that he could begin his rehabilitation as soon as he arrived for training this morning and he is already responding well to treatment,” confirmed Allen.
Gabbidon admitted the injury was a big blow, “Obviously it's a major disappointment for me,” Danny told the official site.
“I hadn't felt my hamstring at all before the actual injury occurred, so it's just one of those unfortunate things that can happen in football.
“I am in good hands with the medical team at West Ham, though, and I hope to be back as soon as possible.”