Johnson suffered the injury during his side's 4-0 defeat at the hands of Nuremberg on Saturday, failing to emerge for the second half after receiving treatment at the break.
The club have not yet confirmed how long Johnson will be out for, but he will miss at least a couple of weeks with the injury.
"Fabian broke his right hand and will be out for some time. As of today, we cannot say how long it will be but surely a couple of weeks before he gets back," Hoffenheim press officer Marc Kennedy told American Soccer Now.
Following the defeat, Hoffenheim sit 13th in the Bundesliga table, just two points clear of the relegation playoff place.