The 6-foot-6 Johnson has appeared in five games since signing his first 10-day deal on March 6, averaging 4.6 points and 20 minutes.
The Bucks are 4-9 since the All Star break and a trade deadline deal that brought point guard Michael Carter-Williams to the rebuilding franchise. At 34-32, Milwaukee remains in sixth place in the Eastern Conference, 4 1/2 games ahead of ninth-place Miami and Brooklyn in qualifying for the postseason.
Carter-Williams was scratched from Saturday's loss at Memphis with a sore ankle. Guards Jerry Bayless and O.J. Mayo have also been limited by injuries.
The Bucks next play Tuesday at New Orleans.