Jonathan Pettibone’s difficult outing in Coors Field on Saturday has led to some speculation that the Phillies might bring Carlos Zambrano to the majors for a start later this week.

Not happening.

General manager Ruben Amaro Jr. said Sunday that Zambrano was not ready to pitch in the majors.

“Not based on what I saw his last outing, not in my mind,” Amaro said. “I’d like to see him pitch again [in the minors]. We’ll keep a close eye on his starts and how effective he is. But he’s not ready yet in my mind.”

Zambrano, 32, went unsigned this winter. The Phillies signed him in mid-May to see if he could provide some depth for a pitching staff that lost Roy Halladay and John Lannan to injury earlier in the season. Lannan has recovered from a quadriceps strain and will return to the rotation Monday night against Washington in Philadelphia.

Zambrano has made four official minor-league starts, two in Single A, one at Double A and one at Triple A. In 21 1/3 innings, he has allowed 14 hits and three earned runs, but he has walked 11 while striking out 17. In his last start at Triple A Lehigh Valley, he allowed four hits and four walks while striking out five in five innings. Scouts who’ve seen Zambrano say his fastball has only been in the mid-80s and he’s relied a lot on off-speed stuff.

“Right now he’s just getting his rhythm back,” Amaro said. “He hasn’t even had what amounts to a full spring training yet.”

Zambrano is 132-91 with a 3.66 ERA in 12 big-league seasons. However, he went 16-17 with a 4.66 ERA the last two seasons with the Cubs and Marlins. He can opt out of his Phillies minor-league contract if he is not in the majors by July 1.