Jackson was signed from Blackpool on a free transfer in June 2008
Shrewsbury Town defender Mike Jackson could be out of action for another three months after seeing a specialist about his knee injury.
Jackson, 35, tore a leg muscle against Luton on 21 February and, despite surgery, has been unable to return.
"Where his cartilage was taken, he now has bruising on top of his tibia," boss Paul Simpson told BBC Radio Shropshire.
Meanwhile striker Grant Holt has been told to rest for the next few days, to ease aching after an ankle operation.
Holt, who scored 20 goals in League Two last season had surgery at the end of May but is expected to return to training before the end of July.
Everyone who's fit will play at least 45 minutes at Northwich, but we are a bit short on numbers
Paul Simpson
Both players miss Shrewsbury's opening pre-season friendly at Northwich on 13 July (kick-off 1945 BST).
Dave Hibbert and reserve keeper Glyn Garner will also be missing and are not expected back in training for the next 10 days, while Shane Cansdell-Sherriff is a doubt as he has picked up a slight groin strain.
"Everyone who's fit will play at least 45 minutes at Northwich, but we are a bit short on numbers," Simpson admitted.
"I'm keeping my eyes open for anyone who could improve the situation, but I won't be busting the budget to do it."
Simpson is still waiting on a decision from winger Chris Humphrey, who has so far refused to sign the new deal offered to him in May.
Bookmark with:
What are these?