ALLEN PARK, Mich. -- When the Detroit Lions drafted linebacker Tahir Whitehead in fifth round in 2012, he weighed barely 225 pounds and the last thing they envisioned was him playing middle linebacker.

But with starter Stephen Tulloch tending to a personal matter Wednesday and Thursday, Whitehead played in the middle with the first-team defense.

"I never played the Mike (middle) until last week, but playing it the last couple of weeks I've been able to get comfortable with it," Whitehead said. "I see myself being able to do it if they needed me to."

Whitehead, one of the team's most productive special teams players last season, weighs closer to 240 pounds now. which is still on the light side for a middle linebacker.

Tulloch weighs 240 pounds, but he's four inches shorter than Whitehead.

"He's an explosive guy," coach Jim Caldwell said. "He's got punch and can run. He can direct traffic in there. He's got a real good feel for the game. He's a good football player. You see his closing speed and the way he makes plays -- Tully is bigger in terms of width and girth -- but (Whitehead) can function in there."

--Receiver Golden Tate was held out of the minicamp because of a shoulder injury.

"It's feeling good," he said. "I'm day to day. It kind of sucks to be out there on the sideline not participating, but I'm trying to make sure I really take some mental reps."

He said sitting out was mostly precautionary and that if this were the regular season he would probably find a way to play. Asked if he would be ready for training camp, he said, "One hundred percent. No doubts about it."

Predictably, Caldwell wouldn't shed any light on the pending contract negotiations with either defensive tackle Ndamukong Suh, who is trying to work out an extension, or rookie tight end Eric Ebron, the team's lone unsigned draft pick.

"I think the way in which this game is, every year is going to be a little bit different," he said. "Not the first guy that's gone through a contract negotiation and it won't be the last. I think those things, Martin (Mayhew, general manager) and Tom (Lewand, president) and those guys and ownership, will do a tremendous job. What I have to do is stay focused on what's happening out there on the field and get our guys ready to play."

A point of reference for Suh: Matthew Stafford didn't sign his extension until July before the 2012 training camp. Ebron has until the start of camp in late July to sign his rookie deal.

Caldwell wouldn't single out any individual performances during the three-day minicamp that concluded Thursday, but he had high praise for the gains made by the offensive line.

"They're a close-knit group and a highly competitive group," he said. "Every one of them is getting a little bit better. (LaAdrian) Waddle's getting better, Larry's (Warford) getting better. I mean, across the board -- they're working at it, but it's a pretty heated competition."

Caldwell said the players were measured in terms of their weight, body fat and general strength from the beginning of OTAs through Thursday.

"The improvement amongst the group was extraordinary," he said. "I mean, they did a great job. So you can tell that they're taking care of their bodies, watching what they eat because our strength gains were great. Guys that needed to gain a little bit more muscle, gained the muscle that they needed, guys that needed to trim down a little bit did so."