The No.8 has not featured this season after shoulder surgery but will play a part when the Warriors head to Musgrave Park to face Magners League leaders Munster on Saturday.
Sean was keen to play the expectation level down ahead of John’s return, he admitted it was a timely boost after Sunday night’s 1872 Cup second-leg defeat to Edinburgh.
The Warriors head coach said in the Evening Times: “Johnnie is a very important player for us and we are delighted he is back in training and that he will play a part on Saturday.
“But while all of that is hugely positive and you are delighted to get any key player of his quality back from injury after five months out, we must temper the expectation level with realism.”
However, Glasgow will still be without Chris Cusiter who is another who has not featured this term.
The Warriors coach said: “Chris is still over a month away and we are hoping that we may have him back before the end of February.
“But I don’t want to put an exact timescale on that. The most important thing is that we get Chris back when he is good and ready.”
In the wake of Ruaridh Jackson’s disappointing kicking display on Sunday, Sean admitted that he is also desperate for teenage stand-off Duncan Weir to make his return from a fractured shoulder.
“Duncan should be ready by the end of the month and that is a positive as Ruaridh has had to shoulder a lot of extra responsibility,” he said.
“All of these injuries to key players have seriously undermined us and it is great to be getting them back.”