Glamorgan's Australian coach Matthew Mott has criticised his former captain, Alviro Petersen, for not honouring an agreement to rejoin the county and abandon his international career.

Essex have confirmed that Petersen will join them for two months next season after he changed his mind about Test retirement and made a successful return for South Africa when he scored a century against Sri Lanka in Cape Town last month.

Mott claimed that Glamorgan still hold a pre-contract agreement with Petersen that he would return to the county this season as a Kolpak player after retiring from international cricket. And as he left a boxing gymnasium in Abercarn, where Glamorgan's players had trained with Wales' former world champion Joe Calzaghe, he was not in the mood to overly trouble himself over whether the agreement was legally binding.

"We feel let down because we had a signed agreement in place, which in my world is binding," Mott told walesonline.co.uk. "We did seek further clarification and he reassured us he was coming. In that time we had let some opportunities go… we stuck with Alviro because of his relationship with the club. But then he changed his mind."

One player Glamorgan chose not to pursue was the Australian batsman, Phil Jacques, who joined Yorkshire instead and who now also has ambitions of achieving English-qualified status.

"After he was picked by South Africa again and made the hundred, we got a little bit nervous about what decision he would make," Mott said. "But we were confident he would still come back because when he had approached us about the Kolpak arrangement last summer, he was a current international. He has chosen to pursue the South Africa route which is fine and we would have understood if he had told us sooner."

Petersen's captaincy season with Glamorgan in 2011 was not without controversy as he infuriated several top umpires with what they regarded as unacceptable power struggles over debatable decisions.

He has joined Essex on a two-month contract as an overseas player in 2012, but hardly endeared himself to his new county when he appeared to suggest on Twitter over the weekend that he would have preferred to rejoin Glamorgan.

To cause further confusion about Petersen's future, Mott said: "He has offered to come as a Kolpak for 2013." Quite what South Africa will make of that is as yet unclear.

Glamorgan are eager to sign Mitchell Johnson, the Australia left-arm quick, as the second overseas player for the Friends Life t20 during the summer. His availability will become clearer after a meeting with Cricket Australia later this month. Johnson is only likely to join Glamorgan if he fails to recover fitness in time to play IPL in April and May.