(CNN) – A foreign policy spokesman for the presidential campaign of Mitt Romney left his job in part because he was restricted from speaking publicly, a source with direct knowledge of the situation told CNN on Wednesday.

The source said Richard Grenell, who was hired to the Romney camp less than two weeks before his departure, was told on several occasions not to speak on the campaign's conference calls with reporters.

The Romney campaign confirmed Grenell's departure on Tuesday.

Grenell's hire was marked by controversy, as he had previously tweeted criticism of high-profile Democratic women, as well as criticism of one-time GOP presidential hopeful Newt Gingrich and his wife, Callista. Social conservatives also criticized the Romney campaign's hire of an openly gay Republican operative.

In a Wednesday interview on CNN's "The Situation Room," Romney senior adviser Dan Senor said that Grenell had apologized for the tweets, and "he certainly wasn't speaking for the campaign."

"Richard Grenell was an extremely talented public servant who worked for four US ambassadors to the United Nations," Senor told CNN's Wolf Blitzer. "I worked with him in the early part of the 2000s and [he] is an extremely talented guy and we were lucky to have him."

In a statement on Tuesday, Romney's campaign manager said they were "disappointed" in the departure.

"We are disappointed that Ric decided to resign from the campaign for his own personal reasons," campaign manager Matt Rhoades said in a statement. "We wanted him to stay because he had superior qualifications for the position he was hired to fill."

– CNN's Mary Snow and Adam Reiss contributed to this report.