The 27-year-old Polish man was discovered at a property in Brothertoft Road, Boston, on Saturday.
Three men, who were arrested on Saturday in Larkspur Croft, where a firearm was recovered, were bailed on Monday.
Chf Insp Paul Timmins, of Lincolnshire Police, said the shooting may have been planned.
"The investigation is at an early stage, however the incident does not appear to have been a random offence and I can now confirm that two outstanding suspects have been located and arrested," he said.
The man has been treated at Queen's Medical Centre, Nottingham.

Police said that shortly after 05:00 BST on Sunday they received reports that six windows had been smashed at the property in the Meadow Park area.
Entry had been gained with damage caused to the interior doors.
At 07:00 BST, police received reports that the property had been set alight causing extensive damage downstairs and smoke damage to the rest of the house.
In the intervening period between the two attacks the occupant of the property had left and no-one was injured.
Police said they had attended the scene and helped to secure the premises following the first incident.

The cases involve 165 suspects and more than 100 victims.
A police spokesperson said many cases had "multiple suspects and multiple victims" but there was also a large number involving single suspects.
Last year, 12 men were jailed for their part in the abuse of a single victim in Keighley.
Eleven were jailed at Bradford Crown Court after being convicted of raping the girl from the age of 13 and another man was sentenced for sexual activity with her.
The CSE figures, which were given to the Keighley News and confirmed to the BBC by police, compare with last year's figure of 220 cases.
There were 261 suspects under investigation at the same time in 2016.
A police spokesperson said: "West Yorkshire Police and partners have been proactive in their approach to encourage victims to come forward and reassure them that all reports will be taken seriously.
"We have developed a far greater understanding of CSE than in the past and this has led to rapid action to prioritise resources to improve the identification and prosecution of perpetrators of this abhorrent crime."

Blades goalkeeper George Long saved Kyle Vassell's first-half spot kick.
Billy Sharp then put the visitors ahead with a low shot, his 20th goal of the season, only for Abu Ogogo to level from Sullay Kaikai's cross.
But Che Adams won it for United, who are four points outside the top six, firing in low from the edge of the box.
Shrewsbury are now without a win in seven games, during which they have picked up just four points out of a possible 21.
Shrewsbury manager Micky Mellon told BBC Radio Shropshire:
"If I'm absolutely honest, which I always try to be, I thought the only team that was going to score was us because we looked like we had the momentum.
"But then a bit of slack defending from a throw-in and we got punished. It was hugely frustrating.
"I couldn't fault much of the performance. We deserved much more than we got, but a bit of loose defending on two occasions cost us."
Two more arrests have been made after a man was found with gunshot wounds in Lincolnshire.
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Extensive damage has been caused to a house in Newtownards, County Down, during an arson attack.
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A total of 179 cases of child sexual exploitation (CSE) are being investigated in Keighley and Bradford, West Yorkshire Police has said.
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Sheffield United kept their slim League One play-off hopes alive by beating Shrewsbury Town, who are just two points above the relegation zone.