McVeigh missed last year's preliminary final win over Geelong because of a minor calf strain and copped a strain opposite leg last week at training.

Longmire told AFL.com.au the 31-year-old could have a significant impact on the team's season when he returned. 

"Obviously both he and the club would rather it hadn't gone," he told afl.com. 

"He'd had an immaculate pre-season with his attention to detail and his work with our physios and conditioning staff, to get his other calf as good as he could, and was training really well. 

"This has set him back but we know he'll do everything he can to get back to peak fitness. 

"Those challenges are always going to be there as you get older, but he's got an enormous amount of experience to draw upon. 

"He's a massive competitor, he's a real professional, and that gives him a chance, and sometimes all that blokes like that need is a chance."

The Swans start the season against Port Adelaide on March 25.