Wellemeyer, 32, was pitching for Triple-A Iowa and appeared in a game on Thursday. He signed a Minor League deal with the team in January.
He was slowed this spring by a right hip injury and was added to Iowa's roster on Thursday. He started that day, giving up four runs on eight hits and two walks over 3 2/3 innings, striking out two.
This was the right-hander's second stint with the Cubs. He was originally drafted by the team in the fourth round in 2000 and spent parts of three seasons with Iowa from 2003-05.
Wellemeyer also pitched for the Marlins (2006), Royals (2006-07), Cardinals (2007-09), and Giants (2010). He finished his career with a 32-34 record and 4.83 ERA in 208 games (75 starts) with 459 strikeouts in 614 2/3 innings.